This hardness tester was made by H W Wallace & Co. Ltd in Croydon, England. It is an analog instrument to quantify the sense of hardness or softness of rubber. A spring load is pressed through a small indenter against the rubber surface to deform it, thus providing a measure of 'hardness' corresponding to the depth of indentation of the rubber. The dial is calibrated in International Rubber Hardness Degrees (IRHD). This is one of the earliest models that include a calibration template.