At the filling station

Jan 28 2019

Pump Accuracy

How do you know you are receiving the correct amount of fuel?

When a pump is installed, it is tested to check that it delivers the correct amount of fuel. When officers check equipment they make sure the measures are within legal tolerances (that is between - 0.5% and + 1%)

The pumps are ‘sealed’ to ensure they cannot be tampered with. Each time any maintenance is carried out or parts need replacing, the testing procedure is carried out again. We also carry out unannounced checks.

The quantity delivered must be within legally defined tolerances. If there are serious complaints or concerns with a pump, then Trading Standards Officers have powers to investigate, issue notices to bring the equipment back to legal compliance or, if necessary, put the pump out of use until the issues are put right.

If you believe a pump you have used is incorrect we would like to hear from you.


  • always check the displays return to zero before starting your delivery
  • if the display advances before you have delivered any fuel replace the nozzle and let the kiosk staff know
  • make sure you are buying the grade of fuel you want. All garages advertise the price of ordinary unleaded fuel on the road side sign. Many also sell a higher grade of petrol, but this is more expensive. Check the unit price displayed on the pump is what you want to buy. The same is true for different grades of diesel
  • note the price to pay when you have replaced the nozzle. This should be the same price as displayed in the kiosk. Sometimes the pump display will jump a penny between finishing delivery and replacing the nozzle. This can happen for a number of reasons and gets more likely as the price of fuel increases

Running up a penny

We sometimes receive complaints from motorists who find that on replacing the nozzle in the pump that the price indicator ‘runs on’ by an additional 1 or 2 pence.

Measurement of fuel in a petrol pump involves the pumped fuel causing a ‘pulser’ to rotate and send a signal to a processor (computer). The customer display shows the quantity delivered and the price as calculated by the computer.

Because the price of petrol is now so high, a very small movement in the pulser can be enough to trip the price indication by a penny or two. In reality, this represents only a very small quantity of petrol – approximately a teaspoonful in fact. The running on can be caused by simply just passing the precise quantity through normal delivery, or when the nozzle is replaced, the internal volume of the hose can change due to internal pressure forcing more fuel into the hose. This effect is called ‘hose dilation’ and is simply the hose swelling slightly. The error in such cases, if any, is very minor and well inside the permitted pump error tolerances of -0.5% to +1.0%.

Before a pump can be put into use in the UK, it must be granted a Type Examination Certificate issued by a Notified Body. Part of the Notified Body’s approval process is that they must be satisfied with the method of price computation.

The solution

As long as the price of fuel remains high, this phenomenon will continue to happen. There is no cure for the problem, but it may be some reassurance to know that as a customer you are not receiving a short measure.

Some garages have ‘penny boxes’ on the counter where some customers place the odd pennies when their transactions have ‘run on’ and that other customers, who are confrontational about the extra penny, take a penny out. This has been found useful in avoiding problems.