It took me some time but finally, I got it !
In the Mileage Calculator language, segment 1 is LUG to ZRH and segment 2 is ZRH to JFK.
You need to make 2 different calculations. One for the outbound flight (with “economy P” for both LUG to ZRH and ZRH to JFK segments) and one for the inbound flight (with “economy Q” for both JFK to ZRH and ZRH to LUG segments).
I’m afraid you made your calculation as if segment 1 was LUG to JFK (via ZRH) and segment 2 was JKF to LUG (via ZRH).
Many thanks to M&M to offer a calculator wich is so difficult to use !!!