I do this when winding two or more pickups to be used in one instrument. Calibration can be done with the winding or the magnetic field. Generally to calibrate the coils for various positions I use a different number of turns and/or desired winding direction for each pickup position. Winding for an instrument with two or more pickups, the bridge pickup usually has more windings than a middle or neck pickup. The bridge pickup could be wound with 8,000 turns, the middle with 7,800 turns and neck pickup with 7,600 turns in a three pickup instrument.