25mm Datum Inserts come in two colours, White with Black Writing or Red with White Writing.
The White / Black Inserts are used to depict the offset measurement of the structure it is fixed to the reference track. The cant of the track is also detailed in 25mm white / black datum plate inserts
The Red / White combination datum plate inserts are used to depict the track in which the measurements are referenced to. and example of this is that is the track that the design is referenced to is the Down Main the Datum Plate would show DM.