The time for using a calculator is well before entering the zone.
On final the wind will be changing on descent. The airplane will be telling you if there's too much x wind (although in a glider you likely don't have the choice of going to another airfield).
Trees, terrain and hangars upwind of the runway can have major influence on the wind.
I recall a Bob Stevens cartoon about a pilot with several different calculators for every conceivable phase of flight. The Salvage Value calculator was put in use at the end of that flight.