> The library has no way to know what the correct
> intermediate unit is.

Yes, that's what I said.

I expected as much.

What lead me to believe that this was possible was the wording in the docs:
"These units include conversions between themselves and the meter.",

I was not sure what the "themselves" referred to, my assumption/hope was clearly wrong.

> You can use BOOST_UNITS_DEFAULT_CONVERSION to specify.
> (Yes, I know this is kind of clunky).

Oddly, given these:

BOOST_UNITS_DEFAULT_CONVERSION(imperial::length_base_unit, si::length);
BOOST_UNITS_DEFAULT_CONVERSION(nautical::length_base_unit, si::length);

Can this please be added to the docs on that specific example.

Thanks Steven and Gavin for the help, exactly what I was looking for.

Regards,