Small ruler (~6 inch) with strange markings. Bought a slide rule

1,842,012 Ruler Stock Photos, High-Res Pictures, and Images - Getty Images

Slide rule - Wikipedia

Slide Rules & Calculators — The National Museum of Computing

224,431 Ruler Vector Images, Stock Photos, 3D objects, & Vectors

Pocket Slide Rule Collectible Slide Rules for sale

National Museum of American History

Pocket Slide Rule Collectible Slide Rules for sale

Slide Rules Were The Original Personal Computers

Slide rules: the early calculators - Chalkdust

I'm Buying Another Empire Combination Square (2020 Gift Guide)

National Museum of American History

Slide Rules Were The Original Personal Computers

What is the Slide Rule? How Well Do You Know Them?

Precision Layout Square, Woodpeckers DelVe SS 6-Inch