Scheduler — the appointment book — Classes and anything shared

Twenty people at one yoga class is twenty bookings at the same time with the same instructor — which, on an ordinary appointment table, is nineteen double-bookings. It is not, and the scheduler needs to be told. Give the view a capacity — a number saying how many the session takes — and it switches to counting seats instead. Bookings sharing a slot stop being flagged, and only genuine problems remain: a class with more people in it than it holds, and one instructor booked into two different things at once. An over-full class is counted once, not once per person — it is one thing to go and solve.