Quickbooks-style date increments/decrements?

I'd like to setup a date field in an Access form, that can be incremented or decremented by pressing the + or - key, respectively, the way it works in Quickbooks. I thought that I could capture the keypress before saving the field, and do the job that way, by using code like this in the OnKeypress event:


Private Sub RequestDate_KeyPress(KeyAscii As Integer)
   Select Case KeyAscii
      Case 43
         RequestDate = RequestDate + 1
      Case 45
         RequestDate = RequestDate - 1
   End Select
End Sub

This seems to work, except that it still types a "+" or a "-" into the box. In fact, if the field value is highlighted, it erases the existing value to do it, although if I hit Esc afterwards, I can see that  the new, correct value, is in place.

How do I get it to just update the field with the new date value, and not insert a + or - into it?