Text box, on update convert text to string, check is numeric, break/if false then set to 1 (or some number) and print an error message/if true then set variable. You could probably leave out the error message and people would probably get the memo if you kept changing the text back to a number and the text box content was implied to be a number.
That was my easy and efficient work around. Sorry for the late response, i just stumbled across this searching about this same issue.