Named derived units

Package: UOM_PACKAGE. Registered by createEngine(); for a slimmer engine, register it explicitly (see choosing packages).

Many physical quantities are really other quantities multiplied together. A force is a mass times an acceleration; power is voltage times current; energy is power times time, or a force times a distance. When you multiply two quantities, the engine tracks what their units combine into, and when the result is one of these named quantities, it shows it by its name:

70 kg * 9.81 m/s^2 as N // 686.70 N
230 V * 13 A as W // 2,990.00 W
50 N * 4 m as J // 200.00 J
2000 W * 3 hours as kWh // 6.00 kWh

N is the newton (force), W the watt (power), J the joule (energy), and kWh the kilowatt-hour (energy again, the unit an electricity bill uses). Writing as N asks for the answer in that unit; the engine also names the result on its own when you leave the as off. This works only where the combination makes a named quantity: 5 m * 3 m is not one of those, so it stays a plain unit product (15.00 m) rather than becoming m², and multiplying two unrelated quantities is still reported as a mismatch rather than invented into a unit. (A fuller algebra of units, and units raised to arbitrary powers, are a later addition.)