The DashComputer's odometer is set to 0 for a new unit. But since the DashComputer will usually be installed into a used vehicle, the first thing that is required is to set the unit's odometer to the correct value. Start by noting the current mileage of your vehicle.
Now download the special odometer firmware available here and flash it into DashComputer as described in the Bootloader section. Turn your ignition off and then on. The DashComputer screen should look like this:
Now, reconnect your terminal program via USB (the USB device gets disconnected with ignition off, so you need to reopen the connection in your terminal program) and hit Enter. The terminal program will ask you to enter the current mileage of your car. Enter the mileage and hit enter. The program will ask you "are you sure?", then hit the 'y' key. The DashComputer should beep and the screen should look like this:
The mileage is now programmed into DashComputer! By the way, since DashComputer's odometer is installed in addition to the existing odometer, you keep the legally required odometer of your car. Even if you remove the odometer LED display (Firebird/Camaro), the odometer is still recorded by the cluster, so if you sell your vehicle you can hook up the LED display again and show the next owner the real odometer.
Setting the configuration
Flashing a configuration is simple: when prompted to enter or update the mileage, hit the escape key in the terminal program. You will now be prompted to upload a new configuration file. The configuration tool generates configuration files with the ".S19" extension, just like the firmware files. Now upload the configuration file using the text upload of your terminal program. The configuration files are really small, so loading the config takes under a second. The program will inform you about success or failure of the upload.
What to do next
After setting the odometer and possibly uploading your configuration you may now proceed to flash the firmware of your choice. The odometer and configuration are preserved across firmware updates, so you'll never have to use this procedure again, unless you move the unit to a new vehicle or would like to update a configuration setting.
Please note: DashComputer's startup splash and background screens are still customized using firmware, so be sure to flash the correct screens into DashComputer that fit the odometer/configuration you programmed!