Heuer Variable Ratio Drive Allows Calibration Of Halda Odometers

In the last few days I purchased a Heuer Variable Ratio Drive from Bruce Gezon, a well-known rally competitor in the USA.   Bruce had recently acquired this unit and had no in-rally experience with the Heuer Variable Ratio Drive.  This is a rare piece of rally equipment that from what I have been able to determine, was not commonly used in the American rally scene.  Perhaps someone will see this post and will be able to add some information about this piece of equipment.  The Heuer Variable Ratio Drive unit is shown below.

Heuer Variable Drive (6)

Heuer Variable Ratio Drive

I believe that this Heuer Variable Ratio Drive unit dates from the days when mechanical odometers, most commonly Halda Tripmasters and Halda TwinMasters, were commonly used in rallying.  These Halda odometers required that users have several gears that would be exchanged inside those odometers to calibrate the odometers with the distance measured by the rallymasters.  Because of the limitation in gearing there always would be a slight error between the measured distances and the distances used by the rallymaster.

The Heuer Variable Ratio Drive attempts to solve this problem, by using a dial to adjust the Halda odometers to almost exactly match the rallymaster’s distance.  The unit works by connecting the input driving cable to the screwed connection shown on the bottom left of the unit.  The output driving cable is connected to the connection on the upper left side of the unit.  The bare steel shaft (seems to be missing a dial) on the bottom right of the unit can be rotated to infinitely adjust the output rotation anywhere between 1.10 and 0.90 times the input rotation. Therefore a rally navigator can get his Halda odometer closely calibrated using the standard interchangeable X and Z gears, then the navigator can fine tune the calibration using the Heuer Variable Ratio Drive by simply adjusting the rotation ratio using the dial.

If you look closely at the image below, then you can see the calibration scale ranging from 0.90 to 1.10.  When I got the unit the scale was held on with tape as shown.  I plan on removing the tape and permanently fixing the scale to unit at a later date.

Heuer Variable Drive (4)

A Closer Look At The Calibration Scale On The Heuer Variable Ratio Drive

Some odometer manufacturers of that era, the Canadian-built Langwell odometer for example, had a similar dial-type calibration method built into them.  This was true with the Mk. IV and Mk. V Halda Speedpilots as well.

It is also interesting that the calibration equation is embossed into the face of the Heuer Variable Ratio Drive.  Very handy.

I have been exchanging emails with David Scothorn in the United Kingdom about this unit.  David is a collector/buyer/seller of Heuer timepieces.  David sent me some information about the Heuer company which provided a potential insight into the Heuer Variable Ratio Drive.  Jack Heuer was relatively young when he was sent to America to assume the presidency of the Heuer Timer Corporation in the USA.  He wanted to expand the Heuer product range beyond just the stopwatch and clock business.  Although I cannot find any direct information about the Heuer Variable Ratio Drive, I suspect that my unit is either a prototype or an early production model for a possible rally-related business line that was subsequently abandoned by Heuer.  Due to a change in business ownership within the Heuer family, Jack Heuer had to return to Europe.  The desire to expand the business beyond just the timing business apparently left with him.  This possible scenario could explain why these variable ratio drives are virtually unknown.

Jack Heuer circa 1958

Jack Heuer Circa 1958

I have just acquired this unit and I have not yet been able to test it.  I need to get the proper cables in order to get it connected to my Halda odometer.  I look forward to seeing how well the Heuer Variable Ratio Drive works on the road.

If anyone can provide additional information about this unit, then please leave a comment below or send me a private email at: shanna12 at comcast dot net

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