What if I need to convert to/from units of a completely different type, like “illuminance”?
A. This is tougher, but you can actually fake a new type by using an existing type. For instance, say you regularly need to convert from lux to footcandles, as 1 footcandle equals 10.764 lux. Create a custom unit for lux, and make it equal to 1 meter. Create a custom unit for footcandles, and make it equal to 10.764 meters. Whenever you convert from lux to footcandles (or vice-versa), the conversion ratio will be accurate. It’s not ideal, but it works.
