Petrol Pump Dip Reading and Tank Stock: The Basics Every Owner Should Know

A dip reading tells you how much fuel is physically in an underground tank. A graduated rod goes down the dip pipe, the wet mark is read in millimetres, and the tank's calibration chart turns that into litres. The point of dipping is the stock check: what the tank should hold, from the last dip plus tankers received minus meter sales, against what it actually holds. The sales hisab (readings, cash, dues) tells you whether the money matches the meters. The dip tells you whether the fuel matches the meters.

How to take a dip

1. Dip at a fixed time, usually at shift handover or once a day at the same hour, and with no sales running from that tank.
2. Wipe the rod dry. Lower it gently until it touches the tank bottom; do not drop it.
3. Lift it straight out and read the wet line in millimetres.
4. Apply water-finding paste on the bottom of the rod now and then; it changes colour where there is water under the fuel. Water litres are not fuel.
5. Convert mm to litres from that tank's own chart. Every tank has its own chart from its calibration certificate; do not use another tank's.
6. Write date, time, tank, mm, litres, and water (if any).

The stock formula

Book stock (closing) = Opening dip litres
                     + Tanker litres received
                     − Meter sales (Closing − Opening − Test litres, all nozzles on this tank)

Variation = Closing dip litres − Book stock

Tank 2 (HSD), 12 Nov 10:00 → 13 Nov 10:00
  Opening dip          8,420 L
  Tanker received     11,960 L
  Meter sales          2,870 L   (two HSD nozzles, tests removed)
  Book stock          17,510 L
  Closing dip         17,470 L
  Variation              −40 L   (loss)

Meter sales here are the same litres you use for the money hisab, with test litres removed, because test fuel went back into the tank. Internal use such as generator diesel drawn through a nozzle is in the meter but was not sold; keep it as a separate line so neither the stock check nor the operator carries it.

Reading the variation

Density and temperature, briefly

Fuel expands when warm, so litres received from a tanker in the afternoon heat and the same fuel dipped on a cold morning will not agree exactly. The oil company's invoice states density at 15°C; your hydrometer and thermometer let you check the delivered product against it. The ranges used in India are roughly 720 to 775 kg/m³ for petrol (MS) and 820 to 860 kg/m³ for diesel (HSD) at 15°C. The density check is about product quality; the dip check is about quantity. Terms explained.

What to keep in the register

One line per tank per dip: date, time, mm, litres, water, tanker litres since last dip, meter litres since last dip, book stock, variation. Keep the refill log next to it. Over a month, the sum of the variation column is the number to watch, not any single day.

Where Fuel Pump Book fits

Fuel Pump Book covers the sales side of this: meter readings per nozzle with tests removed, the money per nozzle and operator, and a refill log with tanker litres and amounts. The meter litres and tanker litres you need for the stock formula are in the app's shift reports and refill list. Dip readings and the stock check itself are not in the app yet; do them in the register as above.