On 22/04/2012 15:32, Clive D. W. Feather wrote:
In message , "
wrote:
I've wondered about that. I've also wondered what those things are
that are mounted from the ceiling that are normally at the end of a
platform. They have a round disk on them, which is angled in such a
way that they are pointing at the train that berths in the station.

Do you mean the small sticks with a yellow disc, about 5cm across? Those
are targets for a laser theodolite and there should be several scattered
around the platform. If there's any significant motion of the tunnel
during reconstruction (even only a couple of millimetres), it can be
measured. They don't face the train, they face the theodolite.

If you mean something else, you'll have to provide a picture.

They are fitted from the ceiling, are always at the front of the
platform and always positioned facing the train.