What are the sliders on rail platforms?

Question

On the vertical part from the platform to the track bed there are panels around 8 x 4 inches with sliders on them. What are these for?

Answer 1

where?

Answer 2

I wondered that too and recently found out. The Slider is set level with the top of the rail, that way when maintainance is carried out on the line, the track is kept at the same level relative to the platform

Answer 3

the engineers use them to measure height... making sure the track bed doesn't sink too much.... otherwise you would have to step up onto the platform from the train... like in the isle of wight...