You can do it with one event like this:

on *:dialog:calc:*:*:{
  if ($devent == sclick) {
    goto $did
    :3 | did -a calc 19 / | halt
    :4 |did -a calc 19 * | halt
    :5 | did -a calc 19 - | halt
    :6 | did -a calc 19 7 | halt
    :7 | did -a calc 19 8 | halt
    :8 | did -a calc 19 9 | halt
    :9 | did -a calc 19 + | halt
    :10 | did -a calc 19 4 | halt
    :11 | did -a calc 19 5 | halt
    :12 | did -a calc 19 6 | halt
    :14 | did -a calc 19 1 | halt
    :15 | did -a calc 19 2 | halt
    :16 | did -a calc 19 3 | halt
    :17 | did -a calc 19 0 | halt
    :18 | did -a calc 19 . | halt
    :22 | did -a calc 19 k | halt
    :23 | did -a calc 19 m | halt
    :24 | did -a calc 19 b | halt
    :20 
    if (!$did(19)) { noop $input(Please specify a calculation in the edit box and click calculate,w,Warning!) }
    else did -a calc 21 $bytes($calc($replace($did(19),k,000,m,000000,b,000000000)),b))
  }
  :error | reseterror
}