CV29 is assigned a single value which chooses a combination of specific effects:
1. Speed step control.
2. Speed table On or Off.
3. Analog mode conversion On or Off.
4. Normal Direction of Travel (NDOT).
5. 2 digit addressing or 4 digit addressing.
Normal Direction of Travel, or NDOT for short, lets you set up your locos to run either long hood forward or short hood forward.
Because with DCC the decoder determines which way the loco will move independent of track polarity, you can set up either direction as forward depending on the prototype.
(Not all decoders have this feature so be sure to check the information that came with your decoder.)
For example, the Southern Railway preferred operating their road switchers long-nose forward for collision protection.
Most railroads preferred short nose forward, for improved visibility.
For most model locomotives, the NDOT would be short nose forward, but for SR units, the NDOT would be long nose forward.