Based on some discussions that were on Facebook recently, I wondered how many people remembered about the Stevens Rally Indicator or as it is often called, the Stevens rally wheel. The Stevens rally wheel is a circular slide rule that was commonly used in the USA rallies in the 1960s and 70s until the electronic calculator became available in a useful size and at an affordable cost.
Stevens Rally Indicator
The Stevens Rally Indicator is a circular slide rule that was a handy means of doing time-speed-distance calculations. It also allows for calibration of the car’s odometer which is a problem when using the car’s standard odometer or perhaps when using even a Halda odometer, if the correct gears are not available to get a suitable calibration with the rallymaster’s measured distance.
The instructions for using the Stevens Rally Indicator are printed on the back of the unit, so you never have to worry about leaving the instructions at home. It only takes short time to learn how to use these units.
Instructions Are Included On The Back Of The Unit
The unit has three arms that are adjustable, but when they are set up, then the arms are locked into the same relative positions allowing for simple and fast time-speed-distance calculations. English and European navigators will note that the Stevens Rally Indicator provides time based on a decimal minute. In other words, the minute is divided into units of 0.01 minutes rather that seconds. Use of a decimal minute allows for much easier calculations when compared to the base 60 mathematics that must be done when working with 60 seconds to a minute.
I have enlarged an image showing the instructions on the back of the Stevens Rally Indicator which explains how the unit is used.
Enlarged, More Readable Instructions
The Stevens Rally Indicator provides incremental times only, therefore if there are changing speeds along a regulatory stage then the navigator has to add the time calculated by this unit to the total elapsed time at the beginning of the section where the Stevens Rally Indicator is being used. These units essentially provide the same information as provided in standard rally tables, but have the advantage of allowing for an odometer that needs to be calibrated to the rallymaster’s distance. Standard rally tables only provide times for the exact distance noted, not for the distance shown on an odometer that is not in sync with the rallymater’s distance.
Stevens Rally Indicators were available in two sizes. The smaller unit is 6-inches in diameter, while the larger unit has a diameter of 9 inches. I have two of the large diameter units, but I have never used a 6-inch diameter unit.
Occasionally these units are seen for sale on eBay. They are useful to use if the rally rules forbid use of electronic calculators and while they are not as powerful as the Curta calculators, they are much easier to use and not nearly as expensive.
There Were 6-Inch (shown here) And 9-Inch (shown above) Diameter Stevens Rally Indicators
If you have any questions or comments about the Stevens Rally Indicator or this post, then please leave a comment below or you can send me a private email message at the following address: shanna12 at comcast dot net