Callback: Wagon length

From GRFSpecs

Wagon length (11)

GRFv≤7 This callback is only called for GRF version 7 and below. GRFv≥8 For GRF version 8 and above use callback 36.

This callback is used instead of train property 21 resp. road vehicle property 23 whenever the vehicle leaves a depot or is displayed inside a depot. If the callback fails, the value of the property is used instead.

The callback result may change only when whole vehicle chain is inside a depot. If your vehicle supports autorefit, and the length can change on refitting, you have to use callback 15E to prevent the refitting.