derive method
Derive SpeedUnits using this SpeedUnits object as the base.
Implementation
@override
Units derive(String fullPrefix, String abbrevPrefix, double conv) =>
SpeedUnits(
'$fullPrefix$name',
abbrev1 != null ? '$abbrevPrefix$abbrev1' : null,
abbrev2 != null ? '$abbrevPrefix$abbrev2' : null,
'$fullPrefix$singular',
valueSI * conv,
false,
offset);