The Telltale Tachometer was never a factory option for MGA, but it would occasionally be installed on one of the MG "Works" competition cars. It was also often used for other competition cars. The red needle could be set somewhere in the vicinity of the intended red line for the engine. If this engine speed was exceeded the white tach needle would push the red needle higher, and the red needle would stay there giving indication of the highest engine speed.

This one is a Smiths Chronometric tachometer, model number and vintage so far unknown. It is installed in an MGA Twin Cam car along with all of the other standard Jaeger instruments. Chronometric instruments are always cable driven. It is common to rotate the instrument in the dash to position the intended red line straight up at top of the dial face where it is easy to see out of corner of your eye without a direct glance.