Charts and diagrams

Roof pitches in degrees, as a rise in 12 (6/12…) and as a percentage, with the rise per metre or foot of run and the rafter factor.

Metric coarse and fine, UNC and UNF thread sizes: pitch or TPI, minor diameter, stress area and the tap drill for each, with the thread it gives.

Amps for common wattages at 230 V and 120 V, 400 V three-phase and 12 V or 24 V DC, and the watts each fuse or breaker size can carry.

The Ohm's law wheel: all 12 formulas for volts, amps, ohms and watts, with a worked example each, plus heating element resistances at 230 V and 120 V.

Celsius to Fahrenheit and back for weather, oven settings, gas marks and body temperature, worked out exactly. Print it for the kitchen.