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.
Some of these resources are old, but still good.
I have attached a paper on current meter maintenance, and a manual for a Price AA current meter made by Rickly Hydrological.
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: