An isometric exercise tool is a device used to exercise most body parts including the wrist and is often used as part of physical therapy or in order to build muscle strength in a low impact manner. Devices can range in size from large bulky machines used by physicians to small hand-held devices that can be used by an individual. Isometric devices have been used for centuries. The first devices did not display the users' output; nowadays there are devices that can digitally output the users force. Before that some devices used an analog format.