Three

Two days at an event, with a queue and no internet

A mela ground, a food stall, and the worst phone signal of the year, because twenty thousand people are standing on it.

1. Before the gates open. Six prices, put in as six buttons. That is the whole setup, and it takes about two minutes.
2. The queue. Tap two buttons, tap Paid. No typing, no searching, no waiting for a screen to load.
3. Paying. Show the UPI QR with the amount already filled in, so nobody stands there typing it wrong.
4. Two people billing. A second phone signs in to the same shop with its own PIN. Both tills add into one total.
5. No signal all day. Every sale is saved on the phone. When you get back to a room with wifi, the whole day goes up at once.
6. After. Two days, split by day, by item and by person, without anyone having counted a single slip of paper.

Try it on an empty till first. Training mode gives you a practice shop that is counted in no report and is deleted when you leave it.