[Spoiler alert]

Ok, maybe I should reveal what’s there then. 

If you look right to the bottom, there are what look like four thin, possibly
square section rules. I thought I could see a joint, and if they were connected,
they’d be consistent with some kind of customs dipping rule, but not an everyday
kind of one.

It was a pleasant surprise when the post person delivered this beauty. A 4-4
side by side format dipping rule by J Gilbert, There were two John Gilberts
(father and son, I believe) working in London in the 18th Century, but I’ve
taken the style of the numbering to be John Gilbert the father, working 1719 to
1750 in Tower Hill.

https://groups.io/g/oldtools/album?id=264874

This rule has quite possibly more data on its surface than any rule of a similar
dimension that I’ve seen. The stats on this are mind blowing.

Two sides, end to end, are almost entirely covered in tables, making upwards of
6.5 feet of data made up of tiny numbers and letters - in this case, look-up
tables of Inches, Parts and either Wine Gallons or Beer Gallons. There are over
2500 individually stamped digits just in these two sides alone. I cannot fathom
how long it would’ve taken back then to complete just one rule, start to finish.

I guess companion instruction manuals weren’t a thing yet, as surely paper would
have been easier. Imagine getting to, say the 2264th digit, and stamping a 6
instead of a 9 ( I believe they used the same stamp back in the day, just
inverted when needed). That leads me to think how many rules like this are
inaccurate, where they made a snafu, and just carried on? I mean, who’s checking
about 3000 digits on each rule in the quality control dept?

So, an interesting discussion piece, and certainly the best £10 I’ve spent in a
while. It never fails to amaze me how bits of history like this wind up at the
bottom of a box of 20th century anonymous every day working tools.