The crystals used in watches are usually cut and selected so that a local minimum or local maximum of the tempco is near the temperature of your wrist. Thus, t

The crystals used in watches are usually cut and selected so that a local minimum or local maximum of the tempco is near the temperature of your wrist. Thus, the tempco is near zero, so human-to-human differences don’t matter much. One thing to notice is that quartz watches almost always have a metal backplate touching your wrist so that the crystal can have good thermal contact. Presumably, the thermometer in your watch was decoupled from that plate.