Why are two bursting ranges quoted on TruBurst verification foils?

The description on the outside of the TruBurst verification foils packet is to help with selection of the most appropriate foils to use to check the instrument.

The label provides details regarding the dome size and the bursting range:

e.g:      Dome 7.3cm²

            Range 160 – 270 kPa

The customer should select a foil which has a range value close to their typical test results and also which correlates with the dome they most frequently use.

Each new batch of foils is tested at James Heal in accordance with specific parameters set through ISO 13938-2 before approval to supply is given.

The exact mean burst result and tolerance are reported on the product information sheet inside the packet,  e.g: 208.5 ±25 kPa

The foils should be burst on the instrument following the same test method as on the product information sheet and the results compared with the exact mean burst result and tolerance as at James Heal.

If the results were to fall outside the exact mean burst result and tolerance, whilst it is within the larger bursting range given for the selection of foils, it would fall outside of the exact bursting range and could indicate a problem with the instrument.