Bank the aircraft and watch the heading turn in real time. The gyro-accurate DG (right) always shows the true heading. The whiskey compass (top strip), free to swing with the local magnetic field, lags the turn approaching North and leads it approaching South — the classic UNOS/ONUS effect. A small red bug on the DG marks exactly where the whiskey compass currently reads, so you can watch the two instruments disagree as you turn.
What's modeled: magnetic dip from latitude (centered-dipole approximation, tan I = 2 tan latitude), a turn rate calibrated so 20° of bank equals 3× standard rate (9°/s), and the compass card's dip/turning error from resolving Earth's field into the banked, yawed card frame. The card is modeled as tilting only a fraction of the aircraft's actual bank (pendulous mounting resists full tilt) — without that, the simplified physics produces an unrealistic reversal at high latitude/bank combinations. This is a teaching model, not a certified training aid.