The ionisation gauge is the only vacuum gauge type for high and ultrahigh vacuum. The pertinent standardisation committee for vacuum technology ISO TC 112 has indicated that important applications need better accuracy, reproducibility and the sensitivity for many gas species, properties which all present types of ionisation gauges lack. This project will provide the relevant parameters for an ISO standard of an ionisation gauge so that this gauge is accurate (total relative uncertainty: 1 %), robust and long-term stable, with known relative gas sensitivity factors, and can be built by any experienced manufacturer.