Back to the math stuff:

I finished my engineering degree with a math minor; I only needed something like 6 more credits to have a double degree in ME and mathematics but was sick of school (and out of money).

I think technically that the majority of trig is planar or constrained to a planar slice of 3D space (unless you're getting into spherical geometry or other non-Euclidian stuff). Algebra plays well in 3 (or more dimensions). I remember calculating some FEA problems by hand where the matrices were ~50 x 50 (which I guess is nothing compared to "real" FEA problems calc'd by software where the matrices are 1000's of elements wide...).

Hardware:

A Keufell & Esser slide rule (plastic) and a laminated aluminum Picket with the extra scales - both with belt holsters of course.

Another Picket with its book and box (no idea where this came from):