You can set up the second field as a calculation field that returns the desired value or you can setup a table of related records where the values for the second field are stored in indivdiual records in this second field. Both approaches work and both are the "best" solution in different circumstances.
The calculation field can be set up with the If function if there are only two possible values for the field or it can be a case function if you need to handle 2 or more values:
Case ( Field1 = "Part-Time" ; 2 ;
Field1 = "Full-Time" ; 3 ;
//add as many boolean expression ; result expression pairs as you need here