Posted By Ron Hunter The most modern electronic gauges (capable of being linked to a stock reconciliation system) are self-calibrating. There is little point, I suggest, in attempting to recalibrate analogue sightglass or dipstick systems, as the capacity of the tank remains, for all intent and purposes, unchanged (barring any sludge build up). More important to follow tanker offloading procedures rigorously, ensure that the tank safe working capacity provides adequate ullage space. Consider tank overfill prevention devices in higher risk situations. The dispensers are more readily capable of calibration of dispensed volume against digital or analogue readout. Your local Trading Standards or pump maintenance company can advise.