Dimensionless units

[David Berry]

Alberto,

> Sorry, but I don't really get the point.
> Apples are apples, and bananas are bananas,
> and the UCDs are clearly stating that those two things
> are not of the same kind:
>
> Jy    ->  phot.fluxDens
> Jy/sr ->  phot.fluxDens.sb
>
> Why would you want to use the units to discriminate between the two?

That's ok if a UCD is always available, but if there are cases where you
want to do unit conversions when no UCDs are available, then you need some
way to distinguish "Jy/sr" from "Jy". Two options I see, one is to use the
unit strings since they obviously differ, the other is to introduce
"pretend" dimensions such as "solid angle", "plane angle", etc, into the
dimensional analysis to supplement the standard M, L and T.

Also, if UCD's are available then why do we need a dimensional analysis
at all since the UCD will imply the dimensions (we would still need the
scaling factor though)?

David