Number 05 – RDWorks Learning Lab 115 – The Russ Formula for Laser Photo Engraving

Transcript of The Russ Formula for Laser Photo Engraving

0:01welcome to another audio works Learning Lab today we’re going to hopefully put a

0:09cap on all this dotty stuff that I’ve been working on for the past few weeks

0:15months I’ve lost track but after a great deal of research that you’ve been

0:20involved with as well I think I’ve come to a conclusion that I can put on a

0:26piece of paper to produce a formula or a formulaic system that will enable you to

0:34get almost perfect dot pictures you’ll have to decide whether or not that claim

0:40is successful by the time we get to the end of this session but I’ve written down here what I call the russ formula

0:50for successful photo engraving and it is a two-page document which sets out all

0:59the steps in a very precise manner with some calculations which you must do and

1:07if you follow these rules you’ll be guaranteed to get a good quality picture

1:13but at the moment I’ve only tested it on white card which basically I class as an organic material

1:19now other organic materials would be things like leather wood NDF

1:26things that burn basically now there is another group of materials which I

1:31haven’t yet tested but we shall have to move into at some stage which what I call mineral materials things like slate

1:38glass granite and then of course there is a third group of materials which basically contains only one material

1:44which is plastic acrylic whether it be coloured acrylic or whether it be clear

1:51acrylic which is what most people will be using so we’ve got these three groups and at the moment I’m only dealing with

1:57the organic but having said that knowing what I know I’m pretty confident that

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

2:04this procedure will work for all three groups so today we’re going to follow this procedure step by step now some of

2:11the steps in here will not need doing multiple times you only need to do the

2:17step once to get the information and once you’ve got that information about your machine you can use that again and

2:24again and again the very first thing that we’ve got to do is choose a lens I would personally always want to go for

2:30the finest lens possible doesn’t mean to say the most expensively it means the

2:35lens with the smallest spot size that I can sensibly use on this machine now on

2:41this type of machine where we have the lens mounted down in the nozzle you can

2:46get a very very short focal length one on a half-inch lens and that’s what I’m

2:51using in this machine on the light blade machines and maybe on your machine as well

2:58there’s a different system the lens is not mounted down here in the nozzle the

3:05lens is actually mounted up here in the stem of this tube now there’s our two each lens sitting in there I know you

3:11can’t get one 1/2 inch lens system for this machine but having said that I have

3:20machined this nozzle out and I’ve adapted this to make a 1/2 inch lens

3:26system that goes on the light blade machine I don’t have to worry about that today because I’ve already got a one 1/2

3:32inch lens in here and that’s what I would advocate you use 2 inch yes it

3:38will work but you might not get such crisp results now the next thing you’ve

3:43got to do is you’ve got to choose the material is going to work with now today

3:49I’m going to be working with a very nice neutral material which is a piece of

3:54card that’s about a millimetre thick but it works extremely well at if you like

4:00taking a good burn and this is the sort of material it most you guys would have experienced if you

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

4:06both spent a little bit of time in the pub because this is just like be a man cardboard now we could use a nice white

4:16I think that’s a spruce plywood which has got virtually no grain or texture on

4:22it at all that’s an ideal material maybe some white maple something like that and

4:29or ndef any of those materials which have basically have got a nice uniform

4:35texture a really good for doing this sort of work on now I’m going to drag

4:41you in to look at this picture of my ex-girlfriend again and because it is

4:47quite important to understand some of the really key principles of doing a dot

4:53picture this background which is white is a very important part of the picture

5:01because there are only two components in this picture there’s white or the

5:07background colour and there’s a dark colour now the dark colour is the dot and

5:14that’s all this picture is made up of it might look like a grayscale picture or a

5:21halftone picture I don’t know what the technical term is but basic to me this is a binary picture because there are

5:27only two elements in it but the success of those elements is the mix between the

5:35background which is light and the dots which are dark

5:41your eye and your brain are very good at ignoring the fact that their dots when

5:47it does a pallet colour mix and creates this grayscale effect so what I’m really

5:56getting to is the fact that it is very important the ratio between the dots and

6:02the background and we can come on to that much more as we get into this

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

6:07process having said we’ve got a white background and black dots there are some

6:15materials that work exactly the opposite way around here’s a piece of clear of acrylic for example and as you can see

6:22when you etch onto a piece of clear acrylic you get white dots now that’s

6:28interesting because it does mean to say that when you come to produce your picture and we’ll talk about this when

6:34we when we go and have a look in our D works you will need to produce your picture and then at the last minute you

6:40will need to make it into a negative so that you’ve got white dots on a well at

6:47the moment it’s a clear background effectively you’re receiving the same results instead of black dots on a white

6:52background you are treating white dots on a black background which is why you

6:57have to turn the process into a negative before you print it I’ve already got this procedure written out on two pieces

7:03of paper and there’s some other information on here like all the calculations and the program that I’m

7:11just about to use if you like to write to me personal message me then I will

7:16gladly send you a copy of this and all the bits and pieces that go along with this procedure that we’re going to use

7:23today well we’ve chosen the right lens

7:29now we’ve also made sure the lens is clean as well I know that my lens is

7:36clean but you might like to check your lens before you start to make sure that it’s really in pristine condition the

7:42next thing that we’ve got to do is to make sure we set the lens to exactly the

7:47right focal point for the surface it’s got to be the sharpest Christmas

7:53dots that we can possibly get and to do that I’ve written a little test program

7:59well it’s not a little test program it’s a little test pattern you will have to program it yourself okay well this is

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

8:06the pattern that I’ve developed and we’ll be using this particular line of

8:12the pattern to assess the quality of our dots as the first stage this is a

8:19multi-purpose pattern and we’ll talk about the other purposes as we get to them this pattern is drawn on a hundred

8:25pixels per centimetre pattern which basically means one pixel is naught

8:31point one of a millimetre so the pixels are point one and the gaps are point one and the reason I’ve chosen

8:38not point one is because it’s typically what you’d expect in a two inch lens for

8:46the spot size now that’s the theoretical spot size ie the smallest possible spot

8:52or dot that you could produce with the two inch lens with a one and a half inch

8:58lens I can get twenty-five percent less if I’m lucky now in practice you’ll

9:05probably find that you won’t be able to get much better than point two with your two inch lens and I won’t be able to get

9:12much better than 0.15 with my one and a half inch lens but we shall see so

9:19hopefully this pattern is also going to be used to allow us to estimate what size the dots are once we’ve produced

9:27the smallest size dots by setting the focus absolutely perfectly now it is

9:32important that we get our material as flat as we can and as you can see this

9:39piece of card is very slightly curved but because I’ve got a steel base plate

9:44here it’s very easy for me to just make sure that that card does sit flat like

9:50that just in case you haven’t done them already or got them I will probably

9:56include these Cutler gauges in in the data pack

10:01so if you write to me you’ll get programs and you’ll get DXF files making

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

10:07these things now I find these incredibly useful these are step gauges because I’ve got one of them that is millimetres

10:17and this one here which is path millimetres so this one runs at five

10:24millimeters here this one is five and a half millimetres and the reason being I’ve just added half a millimetre to the

10:30bottom of this one so you know it was a dead simple gauge and to be honest if

10:35they’re not perfect it doesn’t matter because provided you use these gauges all the time then the correct relativity

10:44between them will remain so something that says five might actually be 5.2

10:50does it matter because every time you’ve set it it’s going to be 5.2 I’ve always

10:56used my one or half inch lens here as having a five millimetre gap beneath the

11:02nozzle so what I’m going to do I’m going to start off at say six millimetres and

11:08I’m going to gradually work my way down to four millimetres so I’m going to take a few readings here start off at six

11:14milliliters don’t it tight I just wanted to slide neatly under this very critical

11:20I’ve got my program set to fifty millimetres per second and at the moment

11:27it’s set to twelve percent power I told you if you blink you’d miss it

11:44okay now unless you’ve got microscopic

11:49eyesight you’re going to need something like this to do the next part of the

11:56test which is to examine these results you don’t need a USB microscope such as

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

12:03I’ve got you can do the same thing in fact you can do it better because you

12:08use natural light with something like this now this is called a linen gauge 210 times magnifier and it sits above

12:16the surface and it’s absolutely perfect for examining these now all the details

12:21on where you can get one of these like on ebay price about 5 pounds for a

12:27plastic version but they’re absolutely perfect for doing this job so I’m just

12:33going to do event a manual assessment of these results and when we get into the office I’ll show you these results under

12:38the microscope for is rubbish 4.5 is

12:45definitely dots 5 looks pretty good

12:535.5 looks remarkably good i’ve got

13:00separation between my dots and six is

13:07not bad either although I think the Ducks beginning to join up just a bit so

13:17I would say that five point five is most

13:23of the dots have got a little gap between them so this is four millimeters

13:29this is four point five you can just see

13:35the beginning of some dots beginning to form just here this is five millimetres

13:41and look we can see some dots coming in

13:47and here we are at five point five and actually the dots are quite well formed

13:55here and they’re compact if we look here you’ll see that this sort of burning and halo around the dots whereas when we get

14:02to here five point five we’ve got nice clean dots but six millimetres look

14:16those dots are beginning to join up so that’s the reason why I chose five point five you can also see from the width of

14:24these lines here that five point five has got thinner lines so there’s two or

14:31three signals on here that tell me that five point five is the correct and the best focus what I’m going to do I’m

14:39going to look at these again on just the five point five to make a visual assessment of the size of the dots now

14:48let me explain that to you I’ve already said that these squares are point one of

14:53a millimetre and the gaps between them are 0.1 of a millimetre therefore if I

15:01can get a point one dot it will sit like this with a distinct

15:07one dot between them if the dots are actually

15:13touching each other like this then the only reason they can be touching each

15:19other is because the dots are actually point to diameter otherwise they

15:25wouldn’t be touching and again we can confirm that by looking in the line

15:31above it because if we’ve got point to point to point to we should also have a

15:39point to gap between them so there are two ways of confirming that we’ve got a

15:44point to dot now if there’s a gap

15:51between these dots then it does mean to say that my dot is smaller than 0.2 but

15:58bigger than 0.1 and so that’s where you’ll have to do a little bit of estimation as to what your dot size is

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

16:04but it is critical that you choose the right size because it does affect the resolution of the picture that we’re

16:10going to be able to produce now it’s very very unlikely unless you’ve got

16:16something like the 4 inch lens and it’s very badly set you’re going to ever see a point 4 diameter dot or burn mark but

16:27again this second row of dots will enable you to see whether or not you’ve

16:32actually got point 4 because if you find two dots like this the touch on this

16:38second row you’ve definitely got point four dots and if you’ve got dots like

16:43this which you’ve got a small gap between them and the gap between them is probably going to be the size of one of

16:50these pixels at the bottom here then that represents 0.3 so we should be able

16:56to estimate anything between point 1 and point 4 size dots with this pattern so

17:02we were looking at point at 5 point 5 for our focus okay now I’ve assessed

17:09these dots and my estimation is they’re not quite touching and so therefore I’m going to call those dots naught point 1

17:168 millimeters diameter we’re now going to talk about resolution of the picture

17:21that we can possibly produce with this size spot because this is the

17:27crucial thing that determines what quality of picture we can actually work with the resolution of a picture is

17:35internationally specified in pixels per each you can get pixels per millimeter

17:42but the standard resolution of the picture is inches but we’re working in

17:47millimeters so what we’ve got to do we’ve got to convert that millimeter

17:52dimension back to pixels per each now there are twenty five point four

17:59millimeters in one each so here we are twenty five point four millimetres one

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

18:06inch and we’ve got to find out how many of these point one eight go into one

18:11inch and the answer is 141 t– t– i so

18:19there we go it’s a very simple calculation to get that dimension back to pixels per inch now that’s the best

18:26resolution of the picture that we can produce with this lens on this material so now we’re going to Rd works and we

18:34will see how we’re going to get this number into our picture now I’ve got

18:39permission to use this lovely photograph because I think it will demonstrate some of the things that we want to show

18:45during this session you can see here that it’s a colored photograph

18:51now when Rd works removes of color this is the end result and it just was far

18:57too dark I could have played with the fairly crude tools in our D works to bring up the lightness in the contrast

19:03but I decided to work on the photograph in another package before I started and

19:09so what we have on the left-hand side here is a slightly exaggerated picture

19:15it is a little bit lighter than you’d normally want it to be it looks as though it’s a bit too bright and

19:21certainly I think if you’re a graphic artist or a photographer you would say well that is a terrible picture well it

19:27may well be a terrible picture to present on a gallery wall but we’re not going to present this on a gallery wall

19:34we’re going to convert this into dots put it down onto a piece of paper or a piece of wood let’s put a bitmap hand

19:40around here and see what resolution this picture is still 600 I’m going to first

19:46of all remove this picture because we don’t need this anymore so we should delete that and then we

19:52want to size this picture and we’ll size that picture by putting a handfuls

19:57around it will close the padlock at the top here and we decide on what size we

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

20:03want this picture to be at the moment it’s very small I think I’d probably like to make that about six inches wide

20:10maybe 150 mil we’ve still got handles around the picture so let’s see if we can get the bitmap handle to work yes we

20:16can and now let’s take a look at the resolution Wow it’s dropped from 600 down to 138 almost where we want to be

20:24if you remember from our previous step we decided that we wanted 141 pixels per

20:30inch we’re now going to set the output resolution to 141 which is the

20:36calculation that we made apply to source okay and we’ll click on here and that’s

20:43turned into a dot graphic as well now okay so now we’re going to have to set the parameters for this picture we

20:51double click on here and open up a parameter box his output yes speed well

21:00we have calculated the speed yet yes we shall have to calculate the speed blowing no we’ll talk about that in a

21:09minute scan yes power I’m going to leave that

21:16at 12 for the moment but we are going to set that to a suitable number when we

21:22get this picture on the machine it’s going to be low and it’s going to probably be between nine and fifteen

21:31percent because that is the high frequency impact region or the pre

21:38ionization zone that your tube will go through before it starts working

21:43properly and that’s the zone that we really want to be working in we don’t want to be

21:48working with and beam we want a high-frequency beam a beam that is not stable that gives us

21:56the best results the interval well we do know the interval because we’ve calculated the dot size and that happens

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

22:03to be point one eighth of a millimeter so we do know that information the speed

22:10we will determine the speed by using a test when we get back to the machine but

22:16at the moment we need to calculate what the speed is yes we are going to

22:22calculate it now here’s where the magic

22:27comes in because this is what we have been striving to find for the past X

22:33number of sessions when we’ve been talking about pixels and that is the

22:39amount of time that it takes for a single pixel to fully form now from the

22:45work that we’ve done with the little picoscope I have established that it

22:50takes between three and four milliseconds for a pixel to form

22:55properly now it might take a little bit of a different time on your machine but I would advise you to probably start off

23:01with this number three milliseconds and then maybe go up to four or five if you

23:07find that it doesn’t quite work for you you won’t have the luxury of a picoscope

23:12to be able to establish exactly what that number is but in my particular instance I feel very confident with

23:18three milliseconds per pixel now if you start pushing the power up to fifteen

23:23twenty thirty percent then that time will go up but we’re not going to go

23:30anywhere near those values we’re going to be staying down at ten eleven twelve thirteen percent power where the time

23:38will definitely be within this three millisecond window so that’s the a magic

23:45number and why I’ve put it at the front of this calculation the first step in our speed calculation is to say look

23:51we’ve got one millimeter and we need to know how many pixels there are in that

23:57millimeter but we know the size of the pixel was 0.18 of a millimeter

24:02so we can do that very simple calculation and find out that we got 5.5 pixels per millimeter now if it takes

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

24:09three milliseconds for a pixel to form three milliseconds times five point five six is sixteen point six five

24:17milliseconds to travel one millimeter now as speed is set in millimeters per

24:26second so we know how long it takes to

24:32travel a millimeter and we know that one second is a thousand milliseconds so if

24:40we take a thousand milliseconds and find out how many 16 point six five milliseconds there are we should find

24:47that we can run at 60 millimeters a second and still allow ourselves three

24:53milliseconds per pixel so now we can go back into our bitmap and we can set our

25:00speed to 60 and the only unknown that we’ve got at the moment is that is the

25:07power and we go back onto the Machine and we look at how we’re going to define

25:12the power now the one thing I nearly forgot to do is that green dot there we

25:22need to go up to config and we need to change that dot from the top left hand

25:29corner to the bottom left hand corner in my particular instance if you happen to

25:35be working up here at the right hand corner as a datum then I would put it down at the bottom right hand corner but

25:40down at the bottom somewhere and I’ll explain that when we get to the machine

25:46we’ve already determined that from our dot size which is 0.18 the best

25:51resolution picture that we can work with is 141 pixels per inch now you may decide to ignore that and so

25:58I’ll tell you what I’ll do I’ll get a better quality picture if I go up to 282 let’s just double it for example well

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

26:05here I’ve got a picture which is 282 pixels per inch

26:12okay now these dots are obviously not

26:200.9 of a millimetre diameter because we’ve got twice the resolution hey we

26:30can’t get 0.9 dots we’re going to put point 1 8 dots down

26:35on that pattern and here’s what’s going to happen when you put point 1 8 dots on

26:40a pattern that’s too tight you know it’s

26:47a little bit of a mess well yes you’re right it is a bit of a mess but what you can see there’s different densities here

26:54of the colour this is very dark and dense

26:59and this is a mixture of densities here can you see that you know and then

27:04you’ve still got a little bit of white but because that white is nothing like the white that we had on the original

27:10picture the white in the original picture was that but where’s it all done

27:15it’s been hidden by big dots on a tightly spaced pattern 282 pixels per

27:22inch and let’s zoom in and have a look at what’s actually happening here we’ve

27:27got our point one eight dot sitting on top of a 282 pixel clip for each pattern

27:35so at the moment yes it works but look

27:40what happens these big pixels are overlapping and as they overlap it means

27:47I’m going to get a double burn here and a double burn here and I’m getting loss

27:52of white space between my pixels so we’re going to get a tremendous amount

27:58of over burning repetitive burning on single dots now that’s going to create

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

28:06extra depth of burn and this is why you get a 3d feel your picture if you get

28:16the dot spacing wrong and you get your dot sizing wrong you will produce a 3d

28:22feeling picture it’s not 3d what it is is just caused by the fact you over burnt the material and

28:30you’ve gone deeper and deeper and deeper with every one of the burns that you put on these dots so that’s why I’m

28:37emphasizing to you and I can’t emphasize it enough don’t veer away from these

28:42rules well we’re back to our chess patent again now because we want to do

28:47now that they determine what power we’re going to be using okay so we’ve got to

28:52run one two three four we’ve run six tests and what we’re going to do is we’re going to look at the relative

29:00darkness of these dots single dots – the

29:05dashes now these dashes are multiple pixels and with multiple pixels you

29:13don’t have the same problem with a single pixel what’s got to happen in the time scale we’ve got to build up to

29:19maximum power and drop off again and produce a black dot whereas here what

29:25we’re really trying to do is do exactly the same thing produce the same depth of

29:31burn like this if you get the power

29:36wrong what will happen is these here will go up like that and they will never

29:43make full power but these will because what they’ll do after the first pixel

29:49which is what we’ve got there the first pixel they will carry on a day will go

29:54to the full deck so what we’re trying to achieve is this

30:03effect here where we’ve got the same depth of burn on a single pixel that we

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

30:08have on multiple pixels as partly that will be determined by the power so what we’re basically trying to aim for is the

30:16lowest possible power that we can and get matching colored lines and pixels

30:23now I know it sounds a strange concept but when you see the results of this

30:30test you’ll understand what I mean the other important thing to do is we’ve already calculated the speed that we

30:37need to run this test at and if you remember 60 millimeters per second so

30:45what we’re going to do we’re going to run our test now at 60 millimeters a second with these various powers on it

30:59now before you can even go near that with a magnifying glass I think you can

31:05see how the power is changing and it looks as though we get color that

31:12matches and around about 11 percent power now I’m going to put this under

31:17the microphone glass and have a look at it but we’ll also take a look at this

31:22under the microscope so that you can see for yourself my visual assessment says

31:28that 12 is the best balance between the dots and the lines I think you can see

31:36without any shadow of doubt we haven’t got anything decent color here at 9% and certainly the dots and the lines are not

31:44the same colour we go to temp sent no 11%

31:50no you can see the dots are still pretty pathetic and weak in relation to the

31:56dashes 12 well looked at under this

32:02microscope 12 doesn’t look all that good in fact I would say that probably 13

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

32:12or maybe 14 gives a far better match well there’s another piece of

32:18information that might help me here if I look at the dots on this bottom line

32:24they are more joined up from there are 13 percent 13 percent gives a much

32:31cleaner set of dots so I think at the end of the day 13 percent should be the

32:37number now I know this all sounds very calculated and fiddly and that there’s

32:43no art in this anymore what I’ve done I’ve removed the skill level from it by

32:49showing you a method by which you will be able to achieve good results now am I

32:55going to fall flat on my face when we reduce the picture that’s the next stage

33:01so we’ve now decided that we can finally set the power parameter so I’ll load my

33:06program in I’ve got my datum set down here so I need to move my head down to

33:13that bottom left hand corner and I said

33:21I’d let you know why I’ve done that I’m going to make sure I’ve turned my ear assist off I know that there’s enough

33:29air leakage through that valve to make sure the lens doesn’t fog up and what’s going to happen is I’m going to close

33:36the lid which is very unusual for me but once this is running I’m glad to close the leak because I need a cross-flow

33:42bear in mind I’ve got a steel table on here with no holes in it and my air has

33:48got a tendency occasion it will creep down the side here but most of it is going down the back of the machine it’s

33:53busy sucking out to the back of the machine so there will be a cross flow of air over the top of the table and that’s

34:00what I want to happen as the smoke comes off of the surface I want it to be wafted away and drawn back now if it

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

34:07gets drawn back and for some reason or other decides it wants to condense on this lovely white paper and make it

34:13brown well it’s not going to worry me because my picture is now starting at the bottom and so everything that I

34:20leave behind going to have clean air passing over it and when I get to the end of the picture

34:26I’m going to have a pristine result I hope I’m going to knock your socks off with the results of this enough talking

34:33let’s get on with it but we’ll have to close the lid and walk away because it’s probably going to take an hour to do

34:40this picture it’s not a fast process and away we go

34:51you can see they’re drifting up and walking back at the moment [Music]

34:57I’ve open the lead up a little bit more so you see it and there’s still a good cross player across there but when I

35:02close the lid down it will really zip out of there what took about an hour to do but here’s the end result

35:17now the real test to me is whether or

35:22not I can feel any three dienes there’s nothing around there at all that black

35:30is just a little bit sticky so possibly

35:41just possibly I underestimated the dot size so maybe I should have done it at

35:48point two and given a little bit more spacing between the dots because in that black area there that’s the only area

35:56where there’s any hint of a problems but apart from that I think you’ll agree

36:02it’s not a bad copy of the photograph but all the details of these hairs when

Transcript of The Russ Formula for Laser Photo Engraving (Cont…)

36:08her eyes were not particularly bright in the picture but they’re certainly there you can see the pupils in the irises so

36:16yeah I think I’m pretty pleased with that but I did today wasn’t really a fluke because a couple of days ago I did

36:23some similar work on the light blade machine and here’s the result that I got

36:29with a 2-inch lens and here’s what happened when I changed for one a half-inch lens with exactly the same

36:36speed settings and power settings

36:42two-inch lens one of the half-inch lens [Music]

36:48still a good picture but softer less power going into the dots so with the

36:56one and a half inch lens I can get more density more power density into each dot

37:02well as I’ve shown you the rust formula seems to work with two different

37:07pictures three lenses of two machines well if you had to try this for yourself

37:14I’m pretty confident it might work straight out the box but if it doesn’t I’ve explained everything and you’ve got

37:21an idea where you might be able to tweak a few things here and there so enjoy yourself waste a lot of time and I’ll

37:28see you in the next session I know