Why the comparison has to be daily
A stock variance has four common causes and they are indistinguishable from each other in a number: evaporation, a calibration drift on a dispenser, a metering error, and a leak. Three of those are ordinary business. The fourth is an environmental liability and a fire risk.
What separates them is not the size of the variance but its shape over time. Evaporation is small, steady and warmer in summer. Calibration drift is consistent on one nozzle and absent on the others. A metering error is a step change on a date. A leak grows. None of those shapes is visible in a monthly figure, because a month collapses thirty days of signal into one number that any of the four could have produced.
Reconciling daily costs the same effort spread across the month and produces a series instead of a scalar. That series is the whole diagnostic.
The calculation
Opening stock, plus deliveries received, minus litres dispensed by every nozzle on that tank, equals book stock. Book stock minus the measured dip is the variance. Positive means you are holding more than the books say; negative means fuel has left without being sold.
How stock reconciliation works in PumpDesk today
Every tank carries a capacity and a fuel type, and every nozzle is attached to exactly one tank. Each tank also carries a running system figure, which a logged tanker delivery increases automatically against the right tank.
You record a dip per tank per day. PumpDesk stores three things together: the dip you measured, the system figure it was measured against, and the difference between them — captured at the moment the dip was taken, so looking at a past date shows the variance that was true then rather than one recomputed against today.
- Dips are per tank, per day, with the variance stored alongside rather than recomputed later.
- Deliveries top up the correct tank automatically when a tanker is logged against it.
- Low-stock thresholds per tank surface on the dashboard before you run dry mid-rush.
- Variance is shown per tank rather than pooled, so a problem on one tank is not diluted by three that are fine.
What the system figure includes, and what it does not
The book figure starts from the opening stock you confirm for a tank, adds every logged delivery and subtracts the litres your meter readings say were dispensed. So the difference against a dip is a real variance rather than the day's sales wearing a variance label. Two things it still does not model: density and temperature, so a warm afternoon's expansion sits inside the figure, and pump-test litres drawn and returned, which read as a small standing loss. Until a tank's opening stock is set, PumpDesk reports that tank as unknown rather than guessing.
Reading the variance
Rules of thumb are dangerous here, because the honest tolerance depends on your throughput, your climate and the age of your equipment. What is not ambiguous is the direction of travel. Use the table below to interpret the pattern rather than the single number.
| Pattern | Likely cause | What to do |
|---|---|---|
| Small, negative, steady, worse in summer | Evaporation loss | Record it, watch the seasonal curve, take no action |
| Consistent on one nozzle only | Dispenser calibration drift | Get that dispenser stamped and recalibrated |
| Step change starting on a date | Metering error or a reading habit that changed | Check readings either side of the date |
| Negative and growing week on week | Possible tank or line leak | Stop, tightness-test the tank and lines, escalate |
| Positive, then correcting | A delivery logged late or a dip taken wrong | Check the tanker log against the invoice |
Interpreting a stock variance by its shape over time.
Deliveries are part of the same number
A tanker delivery is the largest single event in a tank's day and the easiest one to get wrong, because the invoiced quantity and the quantity that actually entered your tank are two different measurements taken by two different parties.
PumpDesk logs the company, invoice number and litres received against a specific tank, and tops the book stock up by that figure. If the invoice says one thing and your dip after unloading says another, the variance appears on the day of the delivery rather than being smeared across the month, which is the difference between a conversation with your supplier and a shrug.
Frequently asked questions
Do I need a dip chart for my tank?
You need whatever converts your dip measurement into litres for that specific tank — usually the calibration chart supplied with it. PumpDesk records the litres. Converting centimetres to litres depends on the tank's own geometry, and using a generic chart for a tank it was not made for is a reliable way to manufacture a variance that is not there.
What is an acceptable stock variance?
There is no single honest figure, because it depends on throughput, ambient temperature and equipment age. What matters more is that the variance is stable and explainable. A pump that knows its own normal band can spot the week it leaves that band; a pump that only sees a monthly number cannot.
Does it handle multiple tanks of the same fuel?
Yes. Tanks are individual, each with its own capacity, dip and variance, even where two hold the same grade. Pooling them would hide exactly the case you most need to see — one tank drifting while its twin is fine.
Can I reconcile stock without entering meter readings?
Not meaningfully. Book stock is opening stock plus deliveries minus dispensed litres, and dispensed litres come from the meter readings. Without them there is nothing to compare the dip against, and the exercise reduces to writing down a number.