Alpy’s debrief shows “~14 turns” for a run — and that tilde is doing real work. Here’s how a phone counts turns, and why any app showing you a turn count without a tilde is overselling its data.
A GPS track is a chain of fixes, each with a heading. Skiing linked turns swings that heading left-right-left in a rhythm, so the app watches for sustained heading swings past a threshold (Alpy uses 30° with hysteresis, so jitter doesn’t double-count) and calls each full swing a turn. Carved GS arcs, skidded snow-plough, snowboard turns — the physics read the same.
What the method can’t see: short-radius turns inside the distance between two GPS fixes. A phone logs a fix roughly every second at ~10 m intervals at speed. Tight slalom turns at 1-per-second blur together; the estimate reads low. That’s why it’s “~14,” never “14.”
Because the trend is more honest than the number. Turn cadence — turns per minute, run by run — barely cares about absolute accuracy: if the method undercounts consistently, the day’s curve still shows the real pattern. Alpy plots exactly that as a Day Rhythm chart, and with four or more comparable runs it will tell you your cadence faded 22% from the morning — the legs knew before you did. (With three runs it refuses to claim a trend; small samples make confident liars.)
Estimates are fine instruments as long as they’re labeled. The failure mode isn’t imprecision — it’s precision theater.
Turn estimates, cadence and the day debrief are free in Alpy. About.