not that i would recommend it, but here's a funny little method just fyi:

dialog calc {
  ...
  button "/" 47, 25 14 15 10
  button "*" 42, 40 14 15 10
  button "-" 45, 55 14 15 10
  button "7" 55, 10 25 15 10 
  button "8" 56, 25 25 15 10
  button "9" 57, 40 25 15 10
  button "+" 43, 55 25 15 21
  button "4" 52, 10 36 15 10
  button "5" 53, 25 36 15 10
  button "6" 54, 40 36 15 10
  button "1" 49, 10 47 15 10
  button "2" 50, 25 47 15 10
  button "3" 51, 40 47 15 10
  button "0" 48, 10 58 30 10
  button "." 46, 40 58 15 10
  button "k" 107, 10 69 15 10
  button "m" 109, 25 69 15 10
  button "b" 98, 40 69 15 10
  ...
}

on *:dialog:calc:sclick:42-109:{ did -a calc 19 $chr($did) }

edit: haha, just realized the buttons' text are precisely what you want to add to the editbox. a range check + $did($did).text would also suffice, and would be much more sensible than renumbering your controls:

on *:dialog:calc:sclick:3-12,14-18,22-24:{ did -a calc 19 $did($did) }