I already replied separately to Tom, but since there is a little more to
this than has appeared, here goes (in abbreviated form).
Before the advent of electronic/computerised rally calculators, Halda
basically had the market to themselves. There were three basic models
which they marketed..firstly the SpeedPilot, in several (gradually
improved) versions, followed some years later by the TripMaster (one
readout) and its bigger brother the TwinMaster (two readouts). All were
mechanical instruments which incorporated a speedo cable type distance
input. For basic rallying, this was provided by inserting a Tee into the
normal speedo cable on the back of the speedometer. For more
sophisticated rallying, a separate drive was provided, usually sourced
from a non driven wheel to eliminate wheel spin in reading distance.
The SpeedPilot had two dials on its face, one for setting the required
average speed, and the other a normal clock face with an extra minute
hand. It was in fact a mechanical computer, since it calculated the time
which should have been taken to cover an input distance (cable input) at
a chosen speed (set on the dial by the navigator), and fed this time to
the extra hand on the clock. If the extra minute hand was set directly
over the normal minute hand at the start of a time/speed/distance
section, then to stay on time, the car needed to be driven so as to keep
the two hands lined up. One other important feature of the SpeedPilot
was the distance read out, and the adjustment feature which permitted
the distance read (and used in calculation) by the SpeedPilot to be
matched to the rallymaster's distance, thus saving an inordinate amount
of calculation by the navigator.
The Twin and Trip Masters were not computers at all...merely quite
sophisticated odometers whose readings could be adjusted, by means of
two easily changeable gears, to match a rallymaster's distance to
something like one tenth of one percent....more than adequate for the
task at hand. A navigator's kit always included the two sets of gears
(six or seven small ones, about thirty large ones) which would enable
him or her to adjust from something like 50% to 200% of normal statute
reading with the indicated accuracy.The difference between the two
devices was that the Trip version had only one readout, while the Twin,
naturally, had two readouts. The readouts could be made to run forward
(on route) or backward (usually off route), and in the twin version,
could be run independent of each other, though of course using the same
basic input (useful for keeping track of total mileage and incremental
mileage). If one used a trip master or twin master for an odometer, then
they usually also used a Curta calculator (pepper grinder) for time
computation....but that's another explanation.
John Slade
Former rallyist
Manotick, ON
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