On Thu, Mar 3, 2011 at 2:38 PM, Matthias Schabel <boost@schabel-family.org> wrote:
"implicit conversion between quantity<Unit1,Y> and quantity<Unit2,Z> is allowed if Unit1 reduces to exactly the same combination of base units as Unit2 and if Y and Z are convertible."
 
Doesn't si::length reduce to the base unit "si::meter_base_unit:unit_type"?  If it doesn't what is the base unit of si::length?

base_units and base_dimensions represent the "basis vectors" for units/unit systems, so no. If you look in boost/units/systems/si/length.hpp you can see that si::length is unit<length_dimension,si::system>. I'm still uclear on what you're trying to accomplish. Why don't you give a code snippet that does what you want to do?

Matthias