The number of small businesses who (1) are not currently using Square and (2) are happy using $EXISTING_POS_SYSTEM and won't be convinced to use Square anytime

The number of small businesses who (1) are not currently using Square and (2) are happy using $EXISTING_POS_SYSTEM and won't be convinced to use Square anytime soon and (3) would make significantly larger amounts of cash being offered something like Appointment Reminder as a standalone service that integrates with any POS system is a large enough market to feed patio11 and his family for a very, very long time.