PTB's Dielectric-Constant Gas Thermometer (IMAGE) Physikalisch-Technische Bundesanstalt (PTB) Caption PTB scientist Christof Gaiser at PTB's dielectric-constant gas thermometer, which is used to measure capacitance. Credit PTB Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.