Conditional calculated field in pivot table?
 

I wonder if it is possible to create a conditional calculated field in a
pivot table. In higher education, it is typical to define a full-time
equivalent (FTE) undergraduate student as one who enrolls for a courseload of
15 hours in a fall or spring semester or 30 hours annually. If I have a
pivot table with a calculated field that divides the sum of undergraduate
courseload by 15 to derive the FTE by year and semester the numbers are
correct. But if I drag semester out of the pivot table to show the annual
figures, the numbers are incorrect because the divisor is 15 when it should
now be 30 instead. Is there a way to make the divisor be 15 when semester is
in play, but divide by 30 when semester is not in play? Probably not, but I
thought that I would check. Can anyone think of another workaround?