What are these? Numbers, letters and sliders on wall from track to platform

[igloo]

Hi all,

I have been wondering what the things in the attached images are for. They're on the wall from the track up to the platform. I think these were at Reading station, but many (all?) stations between Reading and Brighton had them. They have a few numbers and letters on, and what appears to be a slider. Can anyone enlighten me please?


Thanks
Ian

 

[Class172]

There at my station too - Droitwich Spa. I always thought they were to do with the signalling as Droitwich still has semaphores - I have no idea if this is true or not

 

[sprite]

Can't be that, New Pudsey has them and that line is colour signals.
I was told by my dad (S&T worker) once when I asked that it was something to do with Pway.

 

[DaveNewcastle]

They are Datum Markers.
This question comes up every few months. Last thread on these was here.
The adjustable marker is used to precisely record the height of the top of the railhead, which is referred to whenever track is being re-laid, tamped or in any other way maintained or adjusted.
They appear on all platforms, bridges and other structures, and without them, there would be no reference for determining that the gauge of the track is within its limits.

 

[igloo]

Aha, many thanks!

 

[Class172]

Aha, many thanks!

and from me

 

[Nym]

Also for the entire length of all electrified routes.

 

[ralphchadkirk]

As DaveNewcastle said, they're datum plates and they indicate the line (in the OP's photo the UM will mean Up Main), the superelevation of the line. The red marker shows the height of the highest rail.
I can also tell you, from personal experience, the letters and numbers are a bugger to get in the plate.

I think that when the knob is green it means that the track must be at the specified design - due to clearances, whereas red means it can be moved and the information on the plate changed.

 

[PinzaC55]

"I think that when the knob is green it means that the track must be at the specified design - due to clearances, whereas red means it can be moved and the information on the plate changed. "

This used to be denoted in "the old days" by a cast iron "Limit Of Lift" plate. I used to volunteer on Peak Rail and one of these was in the pile of junk at Darley Dale so I fixed it under the bridge at the south end of the station to save it ending up in the skip - is it still there?

 

[miikey]

They are called 'Datum Plates'. They are used to moniter the relative movement of the track in relation to adjacent structures.
Top left number is the number of the datum plate, one below is is the Lateral Offset to the plate. i.e. The distance, in milimeters, from the structure to the running edge of the rail. The next one denotes the line. UM = Up Main, etc.
At the bottom is the designed cant of the track.
They are only used when the track runs closer than 3m from a structure, not on all electrified lines as mentioned above. If the plate was fitted with a Red slider, it shows the track condition at the moment the plate was installed, where as if it was Green it would show the designed track possition.
Where a route hase ABT (Absolute Track Geometry) the whole route must be fitter with datum plates, and the slider will always be green.
Hope this helps.