Once you start looking, it’s easy to see (or think that you see) Melencolia squares in many old drawings.
Suzanne Ellison sent me this 1863 ink drawing of a Sikh carpenter that is in the collection of the University of California. Look at the guy’s feet. One is next to a marking gauge. The other is next to an odd angular thing.
As there is no try square shown in the illustration, it’s plausible that the thing touching the carpenter’s big toe is a simple square with a shaped blade.
— Christopher Schwarz
Could the angles cut in it be used for 45 deg. angles, therefore doing double duty?