A distribution company lives on field sales. Reps bill shops, give free-of-charge stock, collect cash and cheques, take returns and refund on the spot — all day, on the road. When that runs on paper and spreadsheets, nobody can say what a shop owes, what a rep is carrying or what the stock is really worth until someone reconciles it by hand.

Model the money first. Every bill, return, exchange, payment and settlement is a record with a number, a state and an owner, and stock moves through FIFO cost layers so profit is calculated rather than estimated. The rep's phone and the office dashboard are two views of one ledger — and because the next distributor would need exactly the same system, each company gets its own PostgreSQL schema.

The temptation was to build a billing app. The decision was to build the ledger and let billing be one way of writing to it. Anything that moves money or stock — a bill, a return, a payment, a write-off — has to leave the books consistent, including when it is cancelled a week later. That single rule is why commissions reverse themselves and why stock is costed in layers rather than averages.

1. 01Tenant layer — one PostgreSQL schema per distributor, resolved by subdomain, with a platform view across all of them
2. 02Field layer — shops on a map, orders, visits and billing from a phone
3. 03Sales layer — bills, returns and exchanges, each with its own dated number
4. 04Money layer — cash, cheques, bank transfers and credit, verified by the office
5. 05Stock layer — purchase orders, goods received, free-of-charge stock and FIFO cost layers
6. 06Commission layer — rep earnings at the rate in force on the bill's date, reversed when a sale is undone

The rep is at a shop counter with a phone in one hand and a customer waiting. So field screens are short, a button that is switched off says why right above it, and the receipt prints from the phone with no laptop in the car. The office does the opposite job — checking, verifying, settling — and gets dense tables and filters instead.

Zergo Distributors runs its sales on it — reps in the field, the office behind them. A bill printed in a shop, the cash it brought in and the commission it earned are one chain of records, and the same system can serve another distributor without either seeing the other's data.

1. 01In a financial system every undo needs its own record. Editing history is how the books stop balancing.
2. 02Cancellation is the hardest feature to get right, and usually the last one designed.
3. 03Field software is judged at the counter, in seconds, with someone waiting.
4. 04Building for your own company removes the last excuse for not knowing how the work is actually done.