When participating in historic rallying you will need a Tripmaster. Because of the high cost of NOS Halda Tripmasters I preferred the new Brantz Retrotrip 2 from England. It has a speedometer cable sensor and two mechanical counters which can be reset to zero.
Here you can see the gauge mounted on the dashbord next to a DCF77 clock, a mechanical stop watch and a digital triple timer. The home made "Rallye Board" is illuminated and has further conectors for the GTech measurement device and a 12V outlet.