GPS Rally Computer

GPS Rally Computer is a Universal app designed to simplify computations necessary to navigate a traditional time-speed-distance (TSD) automobile rally. The design and implementation is based on specifications outlined by Clarence Westburg and Rich Bireta, commonly know as the Simple Rally Computer or by its acronym SRC. The design mimics in digital form the functionality of the classic Zeron 660 and 880 rally computers.

A TSD rally is comprised of stages set along a route defined by written instructions. The first stage is the Odometer Check stage that allows you to calibrate your car’s odometer with that of the Rally Master’s odometer.

In later stages you will follow a course at a particular average speed that will change from time to time at places that are generally unknown in advance.

In order to drive the course at the prescribed speeds. Odometer measurement is obtained from Apple’s GPS receiver or third-party devices via Bluetooth.

The GPS Rally Computer allows you to do all this and much, much more. For more documentation, download the User's Guide.

Features of the GPS Rally Computer:

  • Clock time in either minutes and seconds to tenths of a second or decimal minutes to thousandths of a minute
  • The clock is a 24-hour clock to simplify computations
  • Distance measurements in either miles or kilometers to either two- or three-digit precision
  • The car's odometer distance measurement may be the same or different than the official rally odometer distance measurement
  • One button click to reset default conditions for starting a rally
  • The internal computer clock can be adjusted to match the official rally clock
  • A "sprocket" button in the top menu bar allows access to the app settings from within the running application including settings for display of certain items
  • Calibrate the car's odometer to the official rally odometer on the odometer check stage via a popup
  • Change average speed (CAST) on a custom popup keypad or button input
  • Preselect the next CAST to simplify the process of changing speed on each stage and setting CAST to zero for transit zones
  • As time passes and as the car's odometer is incremented, the actual speed over the course is compared with the expected speed. The difference in seconds or hundredths of a minute is displayed along with an indication of either "Early" or "Late" to stay on pace
  • Time errors may be displayed in either of two modes selectable in the app Settings
  • Pause or Gain time or take a Time Allowance on any stage or within a transit zone
  • Option to Pause or Gain at user-defined preset seconds or cents
  • Handle off-course corrections to time and distance with Reverse button
  • Record "splits" of time and error at any time with a Split button
  • Record "control" and reset time error and distance to zero and increment next starting time 5 minutes later (distance and time are modifiable) with a Control button
  • Log table that records time, elapsed time, speed, distance, and error for various actions such as splits and CAST changes
  • Set next starting time for the Next CAST and have the time tick down on the master clock and autostart CAST, or override with a manual button click
  • Optionally, use a Dual GPS receiver via Bluetooth to supplement or substitute for the Apple internal GPS

Note: Use of the GPS Rally Computer during any particular rally will be subject to the rules and instructions governing the rally and will likely define your category or class among participants. Some rallies may, in fact, prohibit use of this app. Also, some rallies may have classes strictly for those with Simple Rally Computer (SRC) apps.

For better GPS reception and improved accuracy while rallying, third-party wireless GPS receivers are recommended. This app has been tested with Bluetooth connectivity to a Dual XGPS150A Universal GPS Receiver.

Disclaimer: Continued use of GPS running in the background can dramatically decrease battery life.



changes in version 5.0.6
  • At the start, after the odometer check leg, the 1st CAST happens at a particular point or outmarker, typically at zero distance, and at a particular time. Similarly, after a timed checkpoint or control, the start of the next stage will occur at a particular CAST and time. So, to make certain that teams input the correct CAST and Start Time, the CAST input popup will insert "req'd" in the CAST and Start Time fields. To continue, each field must have a valid input
  • Timed CAST at 1st CAST and at Control must be between T.O.D. -30 minutes and T.O.D. +30 minutes, or 0 minutes for Manual CAST by Unlocking & Clicking. Next CAST must be 0 minutes for Manual CAST or T.O.D. + minutes/seconds only for Timed CAST
  • On the CAST xx.xx button the color is now green to indicate the locked position for the 1st CAST and Curr CAST. When to button is unlocked, the color will change to red and importantly the CAST xx.xx will be the Next CAST. This change was done to allow the driver and navigator to see the Current CAST at a glance and the Next CAST only when unlocked
  • To further emphasize the locked and unlocked positions of the CAST xx.xx button, the words "locked" and "unlocked" have been added beside the icon button
  • The Settings have been relocated to the center of the display. Also, the settings themselves are now saved to a file so that settings you have made will persist even after closing and restarting the app
  • The color of the Control button has been changed to red to reinforce the notion that a Control or Checkpoint is an end of a leg
  • Fixed bug when Start Time is precisely 60:00 or 60.00 minutes
  • GUI tweaks and some added text notes on displays
changes in version 5.0.3
  • Added an option for Pause or Gain at user-defined preset seconds or cents. This will allow rapid Pauses or Gains that are quite common instructions in rallies. The option is available in the redesigned Settings, which is now a popup that can be selected within the app while running
  • The new Settings popup has two options for Measurement Settings (time and distance) and six options for Display Settings to change precision or to display options for time error and pause/gain with presets or pause/gain/time allowance with keypad entry. The Measurement Settings may only be set at before starting the rally while the Display Settings can be chosen at any time
  • Several bug fixes and GUI tweaks
changes in version 5.0.2
  • Fixed bug affecting timing error if you make an early departure from an outmarker
  • Fixed bug affecting timing error if you include a pause, gain, or time allowance within a transit zone
  • Added an option to provide numeric entries in the CAST popup by means of buttons. So, now there are two options: keypad or buttons
  • Various GUI tweaks
changes in version 5.0
  • Major redesign of the app that includes numerous code changes for improved logical flow, for fixing bugs, and for adding features or functionality
  • GUI tweaks and some added notes or label changes to convey more information to the user
  • Added "elapsed time" for each stage to the Log table
  • Added padlock icons to "lock" and "unlock" the "CAST xx.xx" button to prevent inadvertent or unintentional actions that might introduce errors in processing
  • Created separate "Split" and "Control" buttons rather than a combined button in earlier versions. Now, touching the "Split" button will immediately record time, speed, distance, etc. in the Log table. Touching the "Control" button will require a second button click to affirm or cancel the action. This should simplify the process and better distinguish Control actions from ordinary Splits done primarily for informational purposes
  • Pause, Gain, or Time Allowance can be added within a Transit Zone
  • Changed the "clear" button title to "BTZ" for Begin Transit Zone where the CAST should be zero in the view where these edits can be made
  • Distance in the Log table is now displayed to three decimal places
  • Distance in the Log table is now displayed to three decimal places
  • Adapted format for iPhone X to avoid the notch

revised: July 12, 2018