Behavior of inch-and-foot vs foot-and-inch

[sffc]

If the unit is "inch-and-foot", how do we deal with issues such as

1. Which unit gets rounded to integer vs custom precision (Rounding of more-significant units #3)
2. Which unit gets the sign if negative (Negative numbers #6)

Given that we've been proceeding with not supporting unit conversion, I think we should just say that we don't bother with this case and just always apply the sign to the first value and default/integer rounding to all but the last value.