Following multiple complaints about elevation inaccuracies (during Trail Run and Cycling activities), I compared the Instinct against my trusty Fenix3 HR in a controlled test. Placed both devices in the car, drove for 60km and found very small acceptable differences in Distance and Total Ascent numbers. Conducted several more tests along the same lines, similar results. All good.
When the Instinct is worn on the wrist, however, with the sensor opening positioned so close to the skin, sweat and dirt block the sensor opening leading to errors. My daughter rides with the Instinct and on two occasions, one (worn on the wrist) logged significantly lower total ascent than her peers while on her second ride (worn over compression arm sleeve) logged elevation accurately.
Thing is, wearing the watch over an arm sleeve means having to use a chest heart rate monitor instead of the optical one. This appears to be a design flaw that cannot be fixed with firmware!