The price comes out of a formula, not a fixed price list. Area, glass type, edgework and the number of drill holes produce a figure, and mental arithmetic gets it wrong downwards sooner or later.
Offcuts belong in the costing, not in the gut. A sheet yielding three cuts leaves remnants, and without that line every job looks more profitable than it is.
Measuring at the customer's place is the critical moment. Centimetres, a photo and a note must land on the same record as the order, or the wrong pane turns up.
Breakage in transport and fitting is unavoidable. Recorded per job, after one quarter it shows whether the fault lies with the frail, the route or one fitter.
The supplier order depends on lead times measured in weeks. The date given to the customer has to come from the glass delivery date, not from optimism.
Emergency work needs billing of its own. The call-out, the night rate and boarding up with a board are lines to raise and collect before the final pane has even been ordered.