Berth step
Also: step, ca, cb
A train’s headcode moving from one berth to the next, because the train itself moved.
Example
A step: 1A23 moves from berth 0153 to 0155. Made-up berth numbers.
The Train Describer sends a few kinds of message. A step (CA) says a headcode moved from one berth to the next. A cancel (CB) clears a berth. An interpose (CC) puts a headcode into a berth, often by hand. A heartbeat (CT) just says “this area is still here”.
Steps are what show a train moving. On their own they don’t say where on a map that is, which is where SMART comes in.
In Trainiac
Berth steps place trains on the live map within seconds.