Eigenstresses were evaluated by embedding a special spherical stress sensor [8,17] in a cylindrical specimen (diameter of 60 mm and height of about 60 mm) of hydrating cement paste. The sensor consists of two glass marble halves that have been "glued" together (total diameter of approximately 16 mm) with an embedded manganin alloy wire. Manganin has the special property that its conductivity is dependent on the surrounding pressure and temperature of its immediate environment. Thus, by monitoring the conductivity of the manganin wire, the hydrostatic pressure surrounding the marble can be deduced. Calibration was performed in a pressurized oil bath at constant temperature. For this study, temperature increases due to hydration were minimized by placing the cylindrical mold containing the cement paste (and sensor) into a constant temperature water bath. Still, all readings were corrected for the local temperature, which was measured using a thermocouple that was also embedded in the stress sensor. Based on readings made on companion specimens in a previous study , it is estimated that the maximum standard deviation should be on the order of 0.5 MPa for stresses less than 10 MPa in magnitude.