On Thu, Nov 15, 2018 at 11:11 AM Roger Leigh via Boost-users
<boost-users@lists.boost.org> wrote:

On 15/11/2018 15:18, Steven Watanabe via Boost-users wrote:

AMDG

On 11/14/2018 05:04 AM, Matt Vinson via Boost-users wrote:

I am having trouble converting from one derived_dimension to another across systems (imperial to metric).  I'd like to convert, say, lb/in to, say, kg/m.  I thought I would do the following but get a compiler error #:

It's not going to work.  lb is a unit of
force, but kg is a unit of mass.  They are not
compatible and there is no conversion between
them.

lb·f (foot-pounds) is force; lb is mass.

No, lb-f is a unit of Torque. lb is a unit of Force.

Hmm, that pound is primarily unit of force is a news to me. The following is from the UK's Weights and Measures Act 1963:

"The yard or the metre shall be the unit of measurement of length and the pound or the kilogram shall be the unit of measurement of mass by reference to which any measurement involving a measurement of length or mass shall be made in the United Kingdom; and- (a) the yard shall be 0.9144 metre exactly; (b) the pound shall be 0.45359237 kilogram exactly."

To my knowledge, the US still adhere to 1894's update to Mendenhall Order which defined  that there shall be 2.20462234 pounds to a kilogram.

On the other hand, lbf is often used to denote "pound force" unit, with 1 lbf being approximately 4.448N or 0.454 kp.

So Boost.Units should then not be used for cooking recipes as the conversions from pound based to gram based quantities would only work on Earth?

Cheers,

Leon