Calibration

Your iPhone's own magnets throw off the compass. Calibration measures that and takes it out. Do it outside away from metal, ideally every trip. The row shows the date and offset. See Calibration. You can also recalibrate from the North step when you start a caving workout.

Overlay: once, in good light, no survey running. It lines the FLIR's picture up with the iPhone camera so heat lands in the right place in ThermDAR photos, video and scans. The row shows Aligned and the date, or Not aligned. Re-align if the clip moves.

Thermal: calibrate the compass first without the FLIR, clip it on, then measure. The row shows the pull it found (in μT), or None saved. Both always show. Overlay offers Pair or Connect when the camera isn't connected; the offset is greyed out until it is. See Thermal Camera.

Meter: calibrate the compass first without the meter, mount it, then measure. Greyed out until a laser meter is connected. SpeleoMap tells from the readings whether the meter (or the FLIR) is on the phone and takes its pull out. A new compass calibration clears both effects; measure them again. Order: Calibration order.

How finely your Cave Line records movement. Finer is smoother but uses more storage (Cave Line).

How much drift, as a percent of distance, before SpeleoMap suggests you recalibrate. 0.5 to 5%, default 2%. Lower is tighter. What drift is and how to fix it: 1.4 Calibration.

Hand-held lines are never corrected against the compass; ARKit's heading is better. Stow Mode has its own Correction switch (Stow Mode settings), off by default.