A blatant knockoff of Lee Valley's Veritas Pocket Squares (imperial and metric).
See https://www.leevalley.com/ for the real thing.
The tops are chopped off (for ease of printing) so they are actually 1 tick short (ie the 1½" square is actually 1 7/16" tall, the 35mm is 34mm tall).
These squares are quite accurate (printed on my i3 MK3 at 0.15mm layer height) - error no more than the width of a tick mark (distance and angles).
The measurements are from the inside of the hook (or base, ie measuring from the edge of a piece of wood) and the base is ⅛" thick (two ticks, inch) and 3mm thick (three ticks, metric).
My preferred printing orientation is as pictured - ruler to the print bed. If printed as modeled (base to print bed), the ruler ticks can become smooshed as melted plastic sags into the tick.
More on accuracy - “flash” on the edges can effect accuracy so pay attention to that. I checked them with a Mitutoyo machinist square and the 3½" was a bit out of square (the smaller ones were good). 150 grit sandpaper on a flat surface quickly made it light tight to the square.
A Brown & Sharpe adjustable protractor showed the smaller squares angles within a tick mark and the 3½" had about 1° of error.
The author marked this model as their own original creation.