April 2001

"Rallying with the Curta Calculator" from Stimson's Rally Factors

Curta Type I
Curta Type I

Rallying with the Curta Calculator

Copied from Stimson's Rally Factors, copyright 1970 by Sports Car Press, Ltd.
The footnote at the start of this section in Stimson's Rally Factors reads:

[The material in this section has been adapted from A New Guide to Rallying by Larry Reid (New York: Sports Car Press; distributed by Crown Publishers, 419 Park Avenue South, New York, N.Y. 10016; $2.95; copyright 1969 by Sports Car Press, Ltd.; used by permission).]

Although the Curta was not invented specifically for rallying, it might well have been, for it is without question the ideal hand-operated machine for navigators. Manufactured by Contina Ltd., of Vaduz, Liechtenstein, this compact instrument is about two inches in diameter and a little more than three inches high, and it weighs only half a pound. Despite its small size it is not a toy; it is a beautifully made precision machine of remarkable versatility. It of course adds, subtracts, multiplies, and divides. It is singularly useful in rally navigation because it repeatedly adds minutes per mile factors and distance, not only giving the time allowed for any mileage but displaying mileage as well. Moreover it is rugged, and simple to operate.

Curta Model I
Curta Model I

Top View
Here the 11-place answering dial and the 6-place indicating dial show the result of multiplying 645,432 (entered in the setting register) by 639.92 (accumulated in the indicating dial as the crank is turned). The answer, 413,024,845.44, is displayed in the answering dial. this entire operation would take a practiced user only 10 to 15 seconds.
The Curta has three registers, similar to those provided by such conventional desk calculators as the Friden, the Marchant, and the Monroe: a setting register, an indicating register, and an answering dial. To accumulate rally time and distance, you enter the appropriate corrected minutes per mile factor (such as given in these tables) in the setting register by positioning the vertical slides. Turning the operating crank adds this factor to itself as many times as you please and places the total in the answering dial. Meanwhile the indicating dial counts the crank turns and registers the total number in the indicating dial. You have only to keep the mileage figures in the indicating dial matched to your odometer reading; the time allowed for that distance will appear in the answering dial. By shifting the carriage you can readily record tenths and hundredths of miles as well as whole miles.

Nicknamed "The Peppermill" because it looks like one, the Curta lends several refinements to rally navigation. It enables you to run an entire rally using only one watch, and to negotiate any number of speed changes without resetting your odometer. To effect a change of average speed you merely note your odometer reading at the speed-change point, run up the corresponding mileage in the indicating dial, enter the new minutes per mile factor in the setting register, and proceed as before. If you prefer a conventional timepiece to a stopwatch, you can pre-insert your starting time in the answering dial and have your readings in clock time.

Curta Model II
Curta Model II

Front View

This is the larger Curta. The setting register comprises 11 vertical slides. Moving the slide buttons up and down selects the digit desired and displays it at the top of the aperture. The slides are numbered from right to left at the base of the aperture; these position numbers are repeated along the lower edge of the carriage, which is shifted by lifting and rotating. On the top the answering dial (white figures) can be seen. Small buttons can be positioned to mark commas and decimal point. Turning the ring clears either the answering dial or the indicating dial, or both.
If you should go off course, the Curta will cope handily. When you turn around to retrace your route to the place where you left the course, note your odometer mileage and crank it into the indicating dial. Pull up the crank to the subtracting position and flip the reverse button. When you reach the place where you went astray, again crank your odometer reading into the indicating dial. The effect of this "double negative" operation is to add distance while subracting time so that when you get back on the official route the answering dial will show the time you should have been there in the first place. Now return the crank and the reversing button to ther original position. Your only problem now will be to make up the time you have lost.

Pauses are handled by adding the prescribed amount of delay time to the figure in the answering dial (this can be accomplished without disturbing the mileage figure in the indicating dial); time gains are effected by subtracting in the same manner.

Completely flexible, the Curta allows you to calculate ahead and, if the need arises, to reconstruct all or part of your previous computations. If, for example, you discover that you have changed speed at the wrong point on the route, you can make the necessary correction in a few seconds. Curta calculators are made in two sizes. The basic model has an 8-place setting register, a 6-place indicating dial, and an 11-place answering dial; the corresponding capacities of the larger one are 11, 8, and 15. The smaller Curta is entirely adequate for rally work. The larger one, however, has enough room in the setting register to accomodate (at its left end) your odometer error factor, enabling you to accumulate official mileage at the left end of the answering dial while odometer mileage builds up in the indicating dial; thus in rallies where turns or speed changes are identified by official distance, you can pin-point the action points readily.

For more information, current prices, and details of a rental-purchase plan, inquiries should be directed to the importer, Burns Industries, 361 Delaware Avenue, Buffalo, New York 14202.

(NOTICE: The importer information above is quite outdated and no longer correct.)

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