Dairywala or the paper register
The register is not wrong. It is just slow at the two moments that cost you money.
A register keeps up fine while milk is coming in. It falls behind at settlement. Adding a fortnight of entries for two hundred members by hand takes an evening, and a single transposed digit is not visible until a member disputes their bill.
The same entries on a phone are already added. The bill for the cycle is built as you go — opening balance, every litre, goods taken, payments made, closing balance — and it prints on a Bluetooth printer or goes on WhatsApp.
The second cost is the queue. In the register you write the fat, then look up the rate, then multiply. On the phone the analyser puts the fat in and the rate and amount are worked out before the can is off the scale.
You do not have to retype your old register to start. Photograph a page and the rows are read off it and filled in, and you check them on screen before anything is saved.