The firmware revision number is stored in firmware_revision.h and the version numbering scheme is as follows.
The numbering goes as follows:
The version number consists of 3 decimal numbers separated by decimal points.
First number is the version number. A new version number would require a significant rewrite and redesign of the code with a significant number of new and changed features.
The second number is incremented when new features are added.
It will be up to the software authors to determine what features have become available at each version number but the firmware. The firmware team should decide collectively when new features have become stable enough that the revision number should be incremented.
The final number is a build number. Every minor change not adding new features this should be incremented. While this will not affect the operation of tuning software it can be important for determining when firware is out of date and notifying end users that fixes are available.