Display lines from multi line text field as multi choice field

The above solution seems to work.  I have a text warning on the form that all serial numbers must be separated by a comma, and the total number of serial numbers may not exceed thirteen.  Next, I have thirteen formula text fields, each one identifying the "part" before a comma.  In addition, i have thirteen check-boxes, and each one is named to correspond to a single serial number.  That way a user can identify the serial number he/she would like to act upon.