The meaning is literally division. (1.0 * meters) / meters = 1.0
If the expression exactly cancels out all units, then the
result is dimensionless and can be implicitly converted
to a double.
OK, I see. From my perspective, having never used Units this was not quite intuitive if you don't mind me say so. If you would allow me to get a little off topic....
My reason behind switching to units was that I wanted to get rid of implicit assumptions about what unit a quantity is in. I am in a client / server environment and store such vectors coming from a client that uses centimeters as all units. Now I expect further clients and want to be prepared for them to use other units, say millimeters. By using Units I intend to push that translation to the foremost interface of the system and not translate anything behind that.
I have much appreciated the constructor of quantity and the fact that it fails to compile without a unit to give meaning to a scalar. This is an excellent design paradigm and will help eliminate bugs!
qlength q(42.0 * meters);
My problem that led to the above misconception was, that I needed to translate that back and forth to the client. From the client was quite easy:
qlength q(4200.0 * centi*meters);
Looks good enough. But getting the value back in centimeters was not. I tried:
double raw_value_to_send_back = q / centi*meters;
But this won't compile. So I looked into scaled units and typedefed this: