Any way to verify numbers entered on form?

Are there any widgets or methods that can be used to compare and verify a number entry? Example, form has a field for user to enter a 4 digit random number. Once enter (i.e. 1234) this number can not be used again. Next user comes to form, enters (1234) message comes up stating this number has already been used. Is this possible?

This is possible using unique question limit. This feature checks if there is a duplicate entry on the same field upon submitting the form.

Guide: http://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question

Thank you EltonCris, that is the information I needed!

I have added an unique question limit to form field. It works, but if the number is already taken, the message that warns the user is not seen until the form is submitted. Is there any way to have message appear before form submittal?

Unfortunately that is not possible to achieve. It is not possible to show warning message before form is submitted. 

You can increase number of digits that your users need to enter, to lower that chance that same number is entered twice.  

Feel free to contact us if you have any other questions.