NOTHING TO MEASURE

This is a water level gauge used to measure flooding on the Mississippi. The bottom of this column is about even with the top of the levee. It is measured in feet. You may be able to see that the first number is 24. The zero point may be arbitrary. Obviously, the river can rise much higher than the street at the mid level of the gauge. 

I've long thought that the Mississippi breathes over long time scales, in and out, up and down. It's doing a deep exhale at the moment.