London Underground users learn about a small sign

Some travellers are learning about a sign by the London Underground track.

A small sign by London Underground tracks has puzzled many for years. It shows numbers and letters with a slider.

Someone asked about the sign on Reddit. People replied, saying it's a Datum Plate for measuring height and track alignment.

Another person agreed. They said it's like the ones on the National Rail network.

A third person said trackmen use it to ensure the track is level with the platform. The track and slider must be set to level.

If it's not level, the train could collide with the platform. One person's father fitted these many years ago.

A fourth user said some datum plates have red or green sliders.

Red shows the current position. Green shows the designed position.

A YouTube video says datum plates help keep the railways running smoothly.

The coloured block on the plate shows where the track was when it was installed, keeping the train at a safe distance.

A green block shows the ideal track position according to new standards.

Engineers use the plate information and surveying tools to adjust the track for safe travel.

The Railway Shop sells old datum plates and says they are fixed to structures near the track.

The plate details show the track's position relative to the structure, which can be monitored for movement.

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