GPS Twin Odometers

Historic, Classic, or Vintage road rallies may permit digital dual odometers, clocks, and stopwatches. This app combines all three using timers and GPS devices built into Apple mobile devices.

GPS inputs are used strictly for distance measures along the rally route. Also, the displayed accuracy of two decimal places conforms to typical historic, classic, and vintage road rally restrictions.

However, it is possible to interpolate distance to three decimal places. There are tick marks to indicate the second decimal place number centered on the display as well as increments of +0.0025, +0.0050, and +0.0075.

Similarly, time measurements are limited to whole seconds or cents. Time, distance, and mode (discussed below) may be chosen at the start of a new rally by touching the Set button to access app Settings.

A set of buttons allows you to chose the active odometer. The leftmost button activates the lower "interval distance" odometer; the rightmost button activates the upper "total distance" odometer; the center button activates both odometers.

From time to time you may measure time and distance for a stage or a checkpoint and record data by touching the Control button. The time and distance will be stored in a log along with geographic coordinates.

Distance options include subtraction of distance when you travel off course. Direction buttons switch between forward (+), reverse (–), and park (0). Also, you may chose between miles or kilometers.

There are three modes of operation selectable in the app Settings: Regularity mode, Jogularity mode, and Lap mode. In Regularity mode, the stopwatch will be reset to zero each time the Control button is pressed. In Jogularity mode the time split will be recorded but the stopwatch will continue recording. In Lap mode, the tabular display will reset the stopwatch to zero when the Control button is touched and each split time will be identified as a Lap in the table.

Note: Use of the GPS Twin Odometers during any particular rally will be subject to the rules and instructions governing the rally and may define your category or class among participants. Please consult the Rally Master for approval of the use of this app.

For improved GPS reception and accuracy while rallying, third-party wireless GPS receivers are recommended. This app has been tested with Bluetooth connectivity to a Dual XGPS150GPS Receiver.

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


changes in version 2.1
  • Updates to accommodate changes in iOS 13 and 14
  • Changes to accommodate formats of various iPhone and iPad displays
  • Minor code tweaks
  • Removed Facebook and Twitter links
changes in version 2.0
  • Added a continuously scrolling hundredth digit to each of the odometer displays
  • With the scrolling digit display, it is possible to interpolate distance to three decimal places. There are tick marks to indicate the second decimal place number centered on the display as well as increments of +0.0025, +0.0050, and +0.0075
  • The color of active odometer displays now vary with the direction of travel and there is a direction of travel label between the two odometers. These two features have been added to make it easier to determine the active odometer and the direction of travel at a glance
  • To facilitate estimating distance to three decimal places and to smooth the scrolling, the app estimates distance traveled between GPS distance inputs at up to 16 times per second when moving at speeds of 15 mph or greater
  • In order to allow more time for the navigator to interpolate distance, the odometer displays are paused for 5 seconds whenever the Control button is touched
  • Some other GUI enhancements and minor bug fixes

revised: September 15, 2021