The patch is compatible with all mods
To use the patch, follow the usual steps outlined here:
Chronometric tachs were driven by a rotating cable from the camshaft, flywheel, or distributor. They contained a mechanical clock mechanism which timed the number of revolutions by the cable and converted that to rpm for display. See post #38 for more info about this type of tach.
See here for info on the impulse tachometer:
These tachs (Smiths) were used on the E Type Jag so were available in the early 60s or before.
Ignition pulses from the distributor were used to trigger the tach.
"By the late 1950s and early 1960s, electric tachometers became the standard in the industry. The main reason they did so was one of cost, since an electric tachometer can easily cost less than 1/4th that of a mechanical equivalent, and there are no machined parts necessary for operation — only a length of wire. Incidentally, electric tachometers are more accurate, making them far more useful. An electric (or electronic) tachometer is simply a voltmeter. Instead of reading direct voltage from a wire, however, the tachometer reads from the ignition's circuitry.
Since the voltage comes in pulse form from the ignition, the electric tach's needle only moves upward momentarily, following each pulse of current. The greater the number of pulses in a fixed period of time, the further the needle moves, because it is ultimately measuring average voltage.
Properly calibrated, electric tachometers are extremely accurate. If their internal circuitry is designed to limit voltage spikes and extraneous interference, such tachometers are very reliable and will last the life of the car."
In the Grand Prix movie opening sequence, there are two views of how the 1966 F1 tachs moved at 3:45 and 4:04:
In this video of Jim Clark taken at Brands Hatch in 1965, the tach jumps to its new position every 1/2 second or so:
Essentially, the tach circuitry counted the number of pulses over a fixed amount of time, then converted them to rpm for display. The number of pulses over time and the resulting rpm were an average so there was some lag. Tachometers were often called "rev counters" because of their counting mechanism.
Our best guess is that these tachs updated every .5 to .6 seconds.
Edited by Lee200, Nov 08 2018 - 08:16 AM.