White plate with indicator on or near platforms

[fixit_f]

Hiya, this has been bothering me for ages, I wondered if a kind person on here could put me out of my misery.

On railway stations such as London Bridge on the wall leading up to the platform edge you can see small white plates, with what appears to be some kind of slide indicator on the right hand side. These appear at regular intervals, and can also sometimes be seen on bridges.

I wondered if they had something to do with indicating rail height, or something to do with the third rail, or markers used to help out the automated systems on those yellow maintenance/grinding trains - but I'm just guessing.

Anyone know? Please

:roll:

 

[Nym]

Search Datum Plates.

 

[table38]

They are volume controls to adjust the platform announcements

Or they may be these

 

[fixit_f]

LOL @ volume control.

Thanks! I can sleep easy now

 

[Yew]

LOL @ volume control.

Thanks! I can sleep easy now

Aha, did you turn the announcement volume down then? I guess you like near a station?

 

[table38]

They are a bugger to adjust because the slider has to be at rail level, so you actually have to release the screw and move the platform up and down to the right height

 

[Ploughman]

They are a bugger to adjust because the slider has to be at rail level, so you actually have to release the screw and move the platform up and down to the right height

No it doesn't.
You can set it at any declared height above the rail as long as it is stated on the plate.
Most common to use +500mm or + 1000mm.