What about doing it in LostFocus?

If you want to show minus immediatelly, you may try (untested idea):

InteractiveChange

if this.value>0
   this.value = - this.value
endif

>My brain isn't functioning correctly tonight so I apologise up-front for asking this question <s>.
>
>Is there a simple way of forcing a 'minus' sign (at the start/begining of a number string) for numeric data entry where we know that the value is and must be negative (eg., entering a credit balance).
>
>I have looked at the various format/picture clauses but I couldn't see anything that would automatically make a number negative and display the negative sign as you start typing.
>
>Whilst I can think of a few ways of doing this (in the keypress event), I just wondered whether there is a simple way that I may have overlooked.
>
>Thanks!