Abstract: A method and apparatus measures signal intensity and frequency of a laser reference signal over time to provide information regarding laser reference signal reliability.

Abstract: An instrument gauge is described of the pointer output type, especially a tachometer, that includes a display cover limiting observation of the pointer by a first window cut into the cover in the shape of a graphical representation of a proportional relationship between engine performance and revolutions per minute or vehicle speed. The window is oriented such that the pointer position indicates RPM or speed on a cover scale. Engine performance is indicated by the relative position of the pointer with respect to the curved shape of the window established by the proportional relationship. The cover includes a second window of such size and orientation that it permits observation of the pointer only when a critical RPM or speed is reached. A flag fixed to the pointer appears in the second window only at the critical value.