* calc/calc.el (calc-ensure-consistent-units): New variable.

* calc/calc.el (calc-ensure-consistent-units): New variable.

* calc/calc-units.el (math-consistent-units-p, math-check-unit-consistency):
  New functions.
  (calc-quick-units, calc-convert-units): Use `math-check-unit-consistency' when
  `calc-ensure-consistent-units' is non-nil.
  (calc-extract-units): Fix typo.

* doc/misc/calc.texi
  (Basic Operations on Units, Customizing Calc):
  Mention `calc-ensure-consistent-units'.