Rally Calculator.

The Richta Rally Calculator is a software program which is intended to perform the calculations necessary for time-speed-distance road rallies, such as those sanctioned by the Sports Car Club of America (SCCA – It runs on a hand held hardware such as Palm, Apple (iPod, iPhone, iPad) and Android phones and tablet computers.

Check out the documentation

This version supports, at the user’s option, display of calculation results in 0.01 minute increments as well as seconds. It also maintains a database of all legs run and provides the ability to look back, review and edit the calculations for any completed legs. This later feature can be particularly helpful at the end of the event when the team is reviewing their performance on the rally.

Richta was designed and written by a TSD navigator with extensive experience in rallying. The author previously used a Curta mechanical calculator to perform the rally calculations, but the limitations of that device spawned the realization that the functions performed by the Curta could be duplicated and the navigator’s job made easier through the use of current computer technology.

The operating principles and application of the Curta to TSD rally are well documented. A good description of these techniques is available from Rally Racing News (

Throughout the 2004 and early 2005 rally season several short comings of the Curta became apparent to the author. First, speed changes on the Curta can not be executed rapidly. Changing average speed on the Curta requires setting 6 small lugs on the side of the device to the minutes per mile factor (the amount of time it takes to traverse one mile at the desired average speed. The factors are typically determined prior to the rally and copied to the route instruction before the event or during the odometer calibration run. Entry and verification of these factors (small numbers entered while bouncing down the road) is time consuming and error prone. It can be very difficult when several route instructions involving speed changes are to be executed in short order. The navigators can find themselves concentrating on the route instructions (as they should) and entering a checkpoint without a precise calculation as to whether they are early or late.

A second issue arises after a calculation is performed and it must be determined whether the rally team is early or late. Performing rally calculations with a Curta is very accurate. Accuracy to within .01 minute or better is possible when using an accurate odometer that reports mileage to the .01 mile. The Curta output, the calculated time of day at which the rally team should arrive at the indicated mileage, must be manually compared to the time of day clock. The navigator must concentrate to determine whether the team is .01 minute early or .01 minute late and this operation can be mentally exhausting when performed five to ten times per mile over the course of a 150 mile event.

The Richta Rally Calculator was designed and written to overcome these shortcomings of the Curta calculator.