Entering decimal numbers - Problem?

This may be premature, but....

In my forms 3.0 I have number fields with input masks like  999.99
Forms uses this to DISPLAY but apparently does not stop the user from entering say 123.456. It actually carries the .006 in any math operations used on the field (like sub-totals).

What have I done wrong here. Should I use something other than NUMBER as the field type? I recall something like RNUMBER or MONEY in Forms 2.3....

Thanks.

-- 
Daryl Erwin                                     Net Address: derwin_at_mach2.WLU.CA
Computing Services                              Surface Mail: P4-1, Main Campus 
Wilfrid Laurier University, Waterloo, Ontario 
Bus:(519) 884-1970 x2910                                          ... Go Hawks!