How not allow a new record to be added with the same number as any previous records

I have a form which is a continuous form.  On the form is a number field, not auto-number.  The user may enter a 1, a 2, a 3, a 4, etc.  But if for example they have already entered a 3 and they try to enter another 3, I want a message to appear letting them know they already entered a 3 and not allow them to enter another one.

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Use the same technique I recommended in your other thread --- create a unique index on the table and then trap the error in the On Error event and display a "nice" message.  I'm assuming that there is another identifier involved so this will also be a two-field index.  Here's a picture. Indexml

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