Field validation is set up using the Validation condition option in the field editing screen. You do not need validation conditions to check a field is in a fixed range. Numeric, Date and Time entry fields can be automatically validated against upper and lower limits: either defined in MAKEDB for the validating database field; or, in 4.6xx only, in the edit control for the field.
If you set up a validation condition, you may define a field to go back to (set focus to) if the validation fails. If the field to go back to is left at 0 processing returns to the same input field. You may want to specify a previous field if a group of entry fields are closely related and a validation condition invoves several of them.
A calculate always formula for a field is not re-evaluated if input is returned to an input field via the go back to field 0 mechanism. The formula will be re-evaluated if you specify an explicit field number to go back to.