copal or Copal

I am confused as to the use of the term copal. I have seen it in references to
lens board openings, in referecnes to shutters (separate from the lens), and I
have seen it in both upper and lower case.

I found one reference that copal #00 was a 25mm opening.

So what is copal/Copal #0, #1, #3, and #3S and how do they relate to lens
boards.

Thanks
Alan Tippett

So what is copal/Copal #0, #1, #3, and #3S and how do they relate to lens
boards.


Check this link:

http://www.largeformatphotography.info/shutters.html