Andrew,

One Microinch is equivalent to 25.4 nanometers and I don't consider that to be metric.

RUnit.isMetric(this.getDocument().getUnit()) returns true for RS.Microinch or value 8.

https://github.com/qcad/qcad/blob/master/src/core/RUnit.cpp#L145-L155
Returns false for: RS::Inch ; RS::Foot ; RS::Mile ; RS::Mil ; RS::Yard
... and true for all the rest.

Also see last note in: https://www.qcad.org/rsforum/viewtopic.php?f=31&t=9506&p=38295

Not to be confused with RDocument::isMetric() because that returns the measurement system unless that is RS::UnknownMeasurement what is rather impossible with drawings created by QCAD.

Regards,
CVH