Loránd Eötvös, with his colleagues Dezső Pekár and Jenő Fekete from 1906 [1] carried out a series of measurements (EPF measurements) validating the proportionality of the gravitational and inertial masses. In 1986, Fischbach and his colleagues revealed systematic deviations in the measurements. These deviations were slightly above the threshold of error, and were neither reproduced nor explained by later measurements, which were much more precise although they used a different method.
As a result of our analysis of the EPF measurements, we found a possibility of systematic error [2] that may justify repeating the experiments under the improved conditions offered by today's state-of-the-art technical facilities. The measurements are planned to be carried out in the Jánossy Underground Research Laboratory at a depth of 30 m in the KFKI site, under appropriate undisturbed and controlled conditions. The repetition of the EPF measurements will be particularly relevant in the Eötvös Year 2019, which is planned to commemorate the 100th anniversary of the death of Loránd Eötvös. In this paper, we briefly review the background, preparations, and current status of the measurements.