Nothing wrong with an Ice Slush or Boiling water for most but they are the 3 1/2 digit DMM version against a 6 1/2 digit requirement for me
I have been playing with an idea on the bench that needs 0.1C accuracy so I need to be well inside that on my end.
** for Boiling point use Demin water and do the altitude correction thing too for those not in the know!!