Units Converter object performs scale/offset conversions, but can also be used any double-to-double conversion, and contains an implementation to chain multiple conversions together.
No conversion, where convert trivially returns the value.
Allow conversion, but this is a flag that indicates the result should be dimensionless because the Ratiometric units were not convertible.
convert the value in the source units to the target units.
lookup the UnitsConverter object that takes numbers from fromUnits to toUnits. This will chain together UnitsConverters registered via units.registerConverter.