If you need different equations, then math column for each option, and finish with an if-then-else would be good as Petr suggested. Though if, and as in your example, the equation is the same and you just need one value changed, I’d do one if-then-else and one math column.
So you have your choice column. Then you have an if-then-else column that gives a different result for each option from the choice column, and then one math column. In your example, the if-then-else would give -Z for choice PCS, and just Z for option CCS, and then your math column would be XY+(result of if-then-else).