with( Units[Standard] ):

Warning, the assigned names factor and polar now have a global binding

Warning, these protected names have been redefined and unprotected: `*`, `+`, `-`, `/`, `<`, `<=`, `<>`, `=`, Im, Re, `^`, abs, add, arccos, arccosh, arccot, arccoth, arccsc, arccsch, arcsec, arcsech, arcsin, arcsinh, arctan, arctanh, argument, ceil, collect, combine, conjugate, convert, cos, cosh, cot, coth, csc, csch, csgn, diff, eval, evalc, evalr, exp, expand, floor, frac, int, ln, log, log10, max, min, mul, normal, root, round, sec, sech, seq, shake, signum, simplify, sin, sinh, sqrt, surd, tan, tanh, trunc, type, verify

Units[UseSystem]( FPS );

__x__ := 10.0 * Unit(ft) + 10.0 * Unit(cm);