What Do The Yellow "H" Signs Mean?

Mystery Hour

Mystery Hour Question

At the side of the road, there are yellow signs with an H on with two numbers on, marking out a fire hydrant. What do those numbers mean?
Glenn, Romford


** Definitive **
Name: Jim, Hammersmith
Qualification: Hydrant Master
Answer: The figure at the top is the size of the main that feeds that hydrant in millimetres – so 100mm. The lower figure is the distance from that plaque to where the hydrant is in metres.

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