Rallying With a Curta Calculator – Part 5

Now it’s time to go rallying with the Curta.  For this example, let’s assume that you are re-starting after checking into a control.  As you will see, starting from mileage 0.00 is even simpler.  Alternatively you might want to re-set the odometer to zero at the start of the leg, this would be a good strategy if you are running just using the stock odometer.

To get the leg started, you have to enter the starting mileage of the leg, the current reading on the rally odometer, and the start time.

It is always good to get into a pattern when working with a Curta so that it gets to be routine.  I like to develop a standard procedure and order of doing things so that it becomes second nature.

Let’s assume that the starting mileage of the leg is 15.46.  Also, I am assuming that you have re-set the rally odometer also to 15.46 to start the leg to agree with the official rally mileage.   To enter these numbers in the Curta, set the 11th place of the slide entry register (farthest left) to 1.  This is equivalent to an odometer correction factor of 1.000.  Once this is done, enter 15.46 into the white indicating dial.  When this this set up, it will also cause the reading of 15.46 to be entered into the black response dial.

Once this is done, enter your starting time, let’s say 27.00 minutes after the hour.  This is done by adding entering 27000 in the slide entry register and cranking the Curta handle once.  Then set the slide entry register to 00000 and subtract this value.  This will return the mileage readings to 15.46. The image below shows the black response dial and the white indicating dial all set to go.

This is How the Dials Should Look Like When You Start a Leg

 The next thing is to enter the odometer correction factor into the Curta by adjusting the value on the left side of the slide entry register to the odometer correction factor.  Note that some adjustable rally odometers are still not adjusted exactly to the official rally mileage.  For this example, I will assume the the odometer correction factor is 1.005.  Only use four significant fingers for the correction factor.  The image below shows the odometer correction factor entered into the slide entry register.

The Odometer Correction Factor Entered in the Slide Entry Register

The next piece of data to be entered into the Curta, is the time to travel 1.0 mile into the slide entry register.  In our example, the required average speed is 40 miles per hour or the equivalent of 1.500 minutes per mile.  The image below shows this value entered into the Curta.  Enter this data in slide entry register using the slide entry positions 1, 2, 3, and 4.

Desired Speed in Minutes per Mile

Now we are fully ready to go.  If the carriage is set in place two then every turn of the crank will advance the official mileage by 0.10 mile and will display the target time (in minutes and 1/100ths of a minute) associated with that new mileage.  Placing the carriage in position three increases the distance by 1.0 mile per rotation and placing the carriage in position 1, will increase the distance by 0.01 miles.  Using these steps, the Curta will allow for successive timing calculations as you travel down the leg.  Pauses and gained can be accounted for by adding or subtracting the values in 1/100 of a minute as required.

The image below shows the display when the official rally mileage (shown in the white indicating dial) reads 24.46 miles.  At that distance to rally odometer should read 24.50 (shown at the left side of the black response dial) and the perfect time to that distance is 40.50 minutes past the hour as shown at the right side of the black response dial.

The Curta Display at Rally Mileage 24.46 Miles

Novices might think that it is difficult to read number in the Curta that are not always right-side-up.  This really is not a problem as you will find that after about 5 minutes you don’t really notice it.

As you can see, the Curta is a very useful device for keeping you on time in a car rally.  And you don’t have to worry about the batteries running out!

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