The AquaCalc is used with mechanical Current Meters like the USGS style Price AA and Pygmy current meters. These current meters most often use a contact switch to indicate a revolution of the cups. In modern current meters this is most likely a magnetic reed switch, but in older current meters this can be a small wire, often called a “cat whisker” that touches a rotating cam in the current meter switch head. AquaCalc also makes a Pygmy Digital Magnetic Head for the Pygmy current meter. This magnetic sensor uses a Hall Effect sensor, and is designed to work with AquaCalc.
The following picture shows a Price AA magnetic head current meter on a bridge crane for use in suspended measurements
Some of these resources are old, but still good.
The USGS has instructions on current meter maintenance which can be found here: https://water.usgs.gov/osw/pubs/9906attachments.pdf
Other resources are available including this in depth video: https://www.youtube.com/watch?v=EINXEAHYsEI
The USGS has an educational site that discusses discharge measurement in broad terms here:
The USGS has more detailed training materials and a report on Discharge Measurements here:
(The whole report can be downloaded here:
And finally the old “bible” of the USGS Water Supply Division: “Water Supply Papers 2175 - Measurement and Computation of Streamflow”. This has a lot of information and theory: