US system isolated from SI

example/avg_velocity.cpp

@@ -20,8 +20,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <units/physical/si/velocity.h>
 #include <units/physical/cgs/velocity.h>
+#include <units/physical/si/velocity.h>
+#include <units/physical/us/velocity.h>
 #include <iostream>
 
 namespace {
@@ -96,7 +97,7 @@ void example()
 
   // Customary Units (int)
   {
-    using namespace units::si::literals;
+    using namespace units::us::literals;
     constexpr Length AUTO distance = 140mi;        // constructed from a UDL
     constexpr si::time<si::hour, int> duration(2); // constructed from a value
 
@@ -112,7 +113,7 @@ void example()
 
   // Customary Units (double)
   {
-    using namespace units::si::literals;
+    using namespace units::us::literals;
     constexpr Length AUTO distance = 140.mi;  // constructed from a UDL
     constexpr si::time<si::hour> duration(2); // constructed from a value
 

example/hello_units.cpp

@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include <units/physical/si/velocity.h>
+#include <units/physical/us/velocity.h>
 #include <units/format.h>
 #include <iostream>
 
@@ -35,7 +36,7 @@ int main()
 {
   using namespace si::literals;
   Velocity AUTO v1 = avg_speed(220km, 2h);
-  Velocity AUTO v2 = avg_speed(si::length<si::mile>(140), si::time<si::hour>(2));
+  Velocity AUTO v2 = avg_speed(si::length<us::mile>(140), si::time<si::hour>(2));
   Velocity AUTO v3 = quantity_cast<si::metre_per_second>(v2);
   Velocity AUTO v4 = quantity_cast<int>(v3);