A workshop for nomograms
A calculator gives you one answer. An instrument shows you the whole trade.
A nomogram is a paper instrument. Lay a straightedge across two marked scales and it cuts the third at the answer. They ran engineering for seventy years, then pocket calculators arrived and they stopped being made — which was reasonable, and also a small loss, because the thing a nomogram does that a calculator cannot is show you the shape of a problem rather than one number from it.
These are real ones. Drag the red line to use them here, or print one at true millimetre scale and use it with the edge of anything straight.
The collection
Or make your own
The workshop turns an equation into an instrument: products, quotients, powers, sums, differences and reciprocal sums. It refuses, loudly and specifically, anything it cannot draw correctly — a nomogram that looks authoritative and is wrong is worse than no nomogram at all.
The method explains where the geometry comes from, including why the position of the middle scale is not a design decision but a consequence.