AMDG Esben Mose Hansen wrote:

What sort of magic do I have to write to get this sort of thing to work?

=== typedef boost::units::quantityboost::units::si::length length_t;

length_t earth_radius = 3438.461 * nautical_mile; ===

boost::units defines a boost::units::metric::nautical_mile_base_unit in terms of meters, so the numbers and concepts are in the library already. Somehow.

Thanks for any help :)

A base_unit provides a nested ::unit_type typedef. typedef boost::units::metric::nautical_mile_base_unit::unit_type nautical_mile; length_t earth_radius(3438.461 * nautical_mile()); Note that converting between different units is explicit so you can't use the copy construction syntax. In Christ, Steven Watanabe