Monument for the Lowest Point in the Netherlands in Zuidplas

You're standing at the monument to the lowest point in the Netherlands, on the Parallelweg Zuid between Nieuwerkerk aan den IJssel and Moordrecht. Behind you, traffic roars along the A20 motorway. Look at that blue post in the water. It's a gauge seven metres tall, the kind of measuring staff used to read water levels. There's a scale on both sides, and it's set in an aluminium frame that tapers to a point at the top. The whole thing stands on a little platform in the water.