'PWM':'PWM in microseconds',# should be microseconds, this is NOT a SI unit, but follows https://github.com/ArduPilot/ardupilot/pull/5538#issuecomment-271943061
'Hz':'hertz',
'kHz':'kilohertz',
# distance
'km':'kilometers',# metre is the SI unit name, meter is the american spelling of it
'm':'meters',# metre is the SI unit name, meter is the american spelling of it