Extroverts are talkative, and might make wider expressive gestures than introverts.
scientists (!) measure how introverts compared with extroverts personal conversational distance varies, then finds the optimal distance for variously 1) remembered) as well as 2) pleasant conversation.
who would like to communicate better wear the watch. the watch senses conversant personality type and optimal conversation distance
The watch could even have country/culture settings.
The result is 10% happier conversation, or 10% more warranties unloaded, or 10% better flirting.