another quite useful bit of information from diggory's dandy little chart - you might say "hidden in plain sight" - instituted in the 1887 changes; was the dividing of the 20 thousands bore measure into two 10 thou steps. it helps to remember that prior to that time, a gun 19 thou over original bore diameter was still in proof.

"it's a poor sort of memory that only works backwards."
lewis carroll, Alice in Wonderland