Abstract: A joint simulator is provided having a housing with a chamber, a piston, slidable within the chamber, and a shaft rotatable within the housing, the shaft having (i) an end configured to engage a power tool to be tested, and (ii) a threaded end engaged with the piston, whereby rotating the shaft causes the piston to slide within the chamber. Hydraulic fluid fills a section of the chamber formed by a side of the piston and the housing, and computer software controlled pressure and relief valves are actuated to regulate the flow of hydraulic fluid in the chamber, to achieve target pressures. The pressure of the hydraulic fluid creates resistance to rotation of the shaft, thereby increasing the torque relative to the angular increase on the shaft and/or relative to time. The joint simulator is provided with means to determine the angular displacement and torque applied to the shaft.