Early British stamps had “corner letters”.  The sheets contained 240 stamps.  The rows each had 12 stamps (so a row cost a shilling), and there were 20 of them (so a full sheet cost a pound).  In the upper-left of the sheet, the corner letters were “A” and “A”.  In the upper-right, they were was “A” and “L”.  In the bottom-right, they were “T” and “L” (follow?)

Someone took one issue, an issue I collect, and “virtually” reconstructed a sheet (on stocksheets), assembling an example of all 240 corner-letter-pairs.  This is something I’ve been trying to do for a while.

Now, I’m going to do something harder: I’m going to take it apart and figure out exactly which printing plate each came from, exactly what shade each is, and come up with n partial sheets (I won’t know what n is until I get the reference works I borrowed from the APRL).  I expect this to take about 80 hours, but to be immensely rewarding.