my dad is a machinist

he commonly works in 1/1000ths of an an inch, and 1/10000ths of an inch. One of his machines can hold to tolerances in the millionths of an inch. (however, the offsets must be checked and adjusted regularly to account for temperature expansion in the machine.)

My dad uses an old DOS program, DesignCAD 2D, for his design needs.

I've never used a slide rule, but my dad did in school. Obviously, modern technology is better, but I imagine they had their place in the past, along with the abacus. Abacuses are cool, btw.

Regards,
Michael