A sounding scale is set up as follows. Usually there are white stripes of 1 cm thickness on a blue background. The numbers on it are also white. These numbers indicate the tens and are shown by the longest line that is bevelled upwards. The stripes that indicate the five numbers have been slanted downwards. The spaces in between are also 1 cm.

Figure 33: Parts of water level gauges

Above the zero point, the centimetres, decimetres and metres upwards add up and below the zero point, they add up downwards. If only a small part of a level is visible, you can still tell from the numbers whether you are above or below the zero limit.

The top of the level shows what kind of level it is. Often that’s the NAP. But it can also be a level that indicates the water level in relation to the Channel level (KP), Weir level (SP) or Boezem level (BP) or any other level. It is very important to know in relation to which plane the water level is indicated by the level and also the distance of this level from the NAP.