The Jaeger and Smiths Chronometric instruments are a shining example of French and British engineering at its very best!
A quick comparison between Chronometric and Magnetic instruments from the same era reveals a vast array of differences, be it component count, machining tolerances, method of operation or simply the reliability of the readings given, The Chronometric units are truly in a league of their own.
If you take a common magnetic instrument and slightly rotate the unit in hand, you will notice that the pointer sways with the movement, while not an issue in a car, if you fit that unit onto a motorcycle the rotational forces acting on the unit along with the extra vibration will sway the readings.
The rotational forces in an aircraft would play havoc with an RPM reading and if you throw in a few barrel rolls, your magnetic unit would be useless.
To counter the issue of external influence, Jaeger Paris developed the Chronometric mechanism for use in WWI Biplane military aircraft, the mechanism uses a precision measure, hold and release mechanism that is incremented by an oscillating balance wheel such as that found in a timepiece. At all times the pointer is restrained by the mechanism with geared position changes at regular intervals, this gives the pointer its unique stepping movement and total resilience to external forces acting upon the instrument.
The French designed unit was then manufactured by British Jaeger and was used in many vehicle applications the most common fitments being motorcycles and race cars but a few British sports cars such as the MG T Series were lucky recipients.
Smiths Industries acquired British Jaeger shortly after and continued to manufacture the Chronometric units under the Smiths MA and SMITHS trademarks.
Ryan Linley has repaired and restored hundreds of Chronometric instruments from formula race cars, aircraft, motorcycles and indeed the MG T series and is able to offer high quality restorations and repairs at highly competitive prices, give us a call and keep your Chrono ticking!