To see if I understand the library, I want to create metric and imperial systems without using Boost Units predefined systems*.  Conversions between lengths are going well.  Conversion between forces are going well until pounds-force to newtons; line 182 in the link.  What am I doing wrong when lbf will not convert to newtons?

Here is my code:
https://coliru.stacked-crooked.com/a/f5f80d39fbdf8013

Any help is appreciated.

*
//imperial
namespace boost {
namespace units {
namespace us {}}}
//si
namespace boost {
namespace units {
namespace si {}}}