Have you considered turning this TextBox into a NumericOnlyTextBox?
Er, no. The InForm student was too stupid to know that this can be done. When you've convinced Terry Ritchie* to create a full on-line Tutorial for InForm, this student will be the class dunce. In the meantime, I'll look into what you've recommended here, thank you - I have lots of textboxes which have upper & lower limits. I get more & more amazed with InForm: you seem to have thought of everything.
* He's very good at tutorials, as we know.
Richard