Fuel economy

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

Fuel economy says how far a vehicle goes on a given amount of fuel. It is written two ways that measure the same thing from opposite ends, and converting between them is not a plain rescale, so the engine handles the turn for you.

Fuel economy is written two ways that mean the same thing: miles per gallon (mpg), where a bigger number is better, and litres per 100 km (l/100km), where a smaller number is better. One is distance per fuel, the other fuel per distance, so they are opposites of each other, and converting between them means taking one over the other, not just rescaling. That is why it needs its own step, and it is done for you:

40 mpg in l/100km // 5.88 l/100km
6 l/100km in mpg // 39.20 mpg
30 mpg in km/l // 12.75 km/l

mpg is miles per US gallon (the gallon the engine ships). Going between two distance-per-fuel forms, mpg and km/l, is an ordinary rescale, since both count the same way up; it is only the mpg-to-l/100km pairing that turns over.