Abstract: A device for measuring the ability of a human operator to stabilize an inherently unstable system so as to maintain an output signal on a display terminal within a preset limit. The difficulty is automatically increased at a relatively fast rate until the human operator approaches the limits of his ability to maintain the output signal within the limits. The difficulty is then increased at a relatively slow rate until the human operator is no longer able to maintain the output of the testing device within preselected limits. The device is mechanized using a general purpose microprocessor and utilizes binary shifts rather than multiplication or division operations in order to achieve real time operation at a sufficiently fast rate in order to test the limits of human ability.