The bench top vapour pressure tester Grabner VP produces results with a bias towards those obtained with the portable tester Grabner VPS.

The critical DVPE specifications on RFG for various US regions has put extra emphasis in laboratories on the quality of DVPE tests. IIS supports the laboratories by the annual DVPE round robin, always organised well in advance of the summer season.

In this round robin sequence American and European labs participate. IIS particularly looks for possible bias between those groups of laboratories. Repetitive programs over the years showed a suspect bias between Europe and the US, though not yet statistically significant.

Further enquiries to laboratories finally revealed a definite bias between the Grabner VP (used by more European participants) and the Grabner VPS. The bias is -0.2 psi. An internal written communication from Grabner confirms this bias.

The older VP bench top system has a sample introduction valve system which is supposed to cause the bias. Grabner VP users should correct their results with +0.2 psi.