Returns the resulting unit for the output of a compute graph. If the resulting unit is equivalent to exactly one existing unit in the system, it will be returned (for example, a series in Coulombs divided by a series in Volts will return an output of Farads). If the output does not have units (for example, a range output,) the unit result will return noUnitAvailable, and if the computation was not successful, corresponding errors are returned.