How Do I Identify 2/12mm And 3mm On Booklet Panes 804B,806B And 807A

Hi. I need some help trying to understand the difference between 21/2mm and 3mm when it comes to booklet panes 804b, 806b and 807a. Is that measurement to be taken from from the vertical space between the two stamps? I have a bunch of booklet panes on those stamps but I'm just not sure how to make the difference. I'll appreciate it if someone could point me in the right direction.

Thank you

Rafael

Yes, one measures the gap between the two columns of stamps. Here is a pane with 3mm spacing on top of a 2.5mm pane:

Thank you John Becker