A movable condition-responsive member such as a snap-acting dished metal member is mounted in a condition-responsive device to move between spaced dispositions such as between the original and inverted dished configurations of a dished metal member in response to occurrence of selected pressure, force or temperature conditions. The member is arranged to engage and move the device control elements during such movement to perform control functions. A series of artifacts such as laser-melted portions of the metal materials embodied in the member are provided in the surface of the member, typically after the member is assembled in the control device. Each artifact establishes a local pattern of stresses in the member at variance with a pattern of stresses in the member adjacent to the artifacts, and the artifacts cooperate to precisely determine the condition which results in the snap-acting member movement. The member is intially formed and processed in conventional manner to provide the member with intended initial condition-response properties differing by selected value from the properties ultimately to be established in the member, and is tested to display its actual properties as initially formed. The artifacts are each proportioned to modify the condition-response properties by only a small increment of said value and they are formed in sequence, typically after member assembly in the device, as the response of the device is tested to precisely determine the condition-response properties of the member in the device.