Add rack units (U)

core/src/units/builtin.rs

@@ -588,6 +588,8 @@ const IMPERIAL_UNITS: &[UnitTuple] = &[
 	("ramsdens_chain", "", "l@5 rope", ""),
 	("roman_mile", "roman_miles", "l@50 ramsdens_chain", ""),
 	("gunters_chain", "gunters_chains", "l@4 rod", ""),
+	("rack_unit", "rack_units", "[email protected] inches", ""),
+	("U", "", "rack_unit", ""),
 ];
 
 const LIQUID_UNITS: &[UnitTuple] = &[

core/tests/integration_tests.rs

@@ -5940,3 +5940,8 @@ fn test_roman() {
 		Some("100001 must lie in the interval [1, 100000]"),
 	);
 }
+
+#[test]
+fn rack_unit() {
+	test_eval("4U to cm", "17.78 cm");
+}