We have some users that like to print the form versus filling out online so the 0s in the calculated fields print then they line through them or write over them and it becomes a mess.
I have found that using the 'Custom Validation script' on the 'Validation' tab will work when any of the calculations options is used. But since this code is only executed when the form field is recalculated, one needs to clear the form or force the recalculation of the form before one will see the results.
I use the following code:
// if the event value is zero, set the field value to a null string
if ( event.value == 0 ) event.value = "";