Ask an operator which of their sites has a fuel loss problem and they will usually name the busiest one. It moves the most stock, so it has the most litres to lose. But the numbers often point somewhere else, and the reason is the difference between net litres and percentage of throughput.
Two sites, same ‘loss’. Site A pumps 400,000 litres a month and finishes 1,200 litres down. Site B pumps 40,000 litres and finishes 600 litres down. In litres, Site A’s problem is twice the size. As a percentage, Site A is at 0.3 per cent, inside the range that temperature, metering tolerance and dip rounding can plausibly explain. Site B is at 1.5 per cent, five times the rate, and on a quiet site there is far less noise available to explain it. Site B is the one that deserves the phone call.
Why percentages flatter big sites. High-volume sites generate high absolute variances that look alarming in litres but are ordinary in percentage terms. The reverse trap catches small sites: a few hundred litres sounds trivial, but against a small throughput it can be the signature of a real leak or a metering fault. If you only ever look at one of the two numbers, half your network is hiding from you.
What the analysis actually uses. The reconciliation method behind AS 4897 does not run on percentages. It works from litres per day, measured against a fixed detection threshold, roughly 18 litres a day, that applies whether you pump 40,000 litres or 400,000. That is deliberate: a leaking fitting drips at the same rate regardless of how busy the forecourt is. It also means quiet sites get proportionally sharper detection, which is exactly where problems hide longest.
How to read your own reports. Look at both figures every month. Litres tell you the cost. Percentage tells you whether the month is explainable. A big site drifting at 0.1 per cent is a rounding story; a small site repeating 1 per cent in the same direction is a job for someone with a wrench, or a hard conversation.
The busiest site buys the most attention, but attention is not the same as risk. Read the numbers both ways and let the quiet sites speak.
