bug#10554: 24.0.92; No units specified (dimensionless quantities in Emacs Calc)

[Jay Belanger]

>> I'll also change it so that Calc can offer unit systems and composite
>> units as default units, but that should probably wait until after 24.1
>> comes out.
>
> Agreed. This is nothing urgent.

Good; then this part will be taken care of as soon as 24.1 comes out.

>>From a different perspective, I'd say that "dimensionless" is as
> valid a unit as "kg" or "hbar / c". In that sense I'd say that there
> should be a possibility to pass this unit "dimensionless" as an arg
> to calc-convert-units, similar to any other unit that this function
> should use for its final result.

Currently, if Calc is asked to convert part of a units expression, it
will leave any unrequested units unchanged; for example, if 45 mi/hr is
on the stack and the units conversion is called with new units m, then
only the mi will be changed; 45 mi/hr will be converted to 72420.48 m /
hr.  To be consistent, I would think that converting to new units 1, all
of the units in the stack expression would be left alone.

> I'd say that "1" appears to be a natural choice in order to express
> the fact that Calc should obtain a dimensionless number.

I suppose you mean /try/ to obtain a dimensionless number.
Calc could have a command that will convert an expression to a
dimensionless number, if possible, or leave it unchanged, if it cannot
be converted to a dimensionless number.  I'm not sure that "u c" should
do such branching, but then I'm not sure this behavior is what you
meant.

Jay