Many introductory books on electricity try to relate voltage to water pressure, electric current to water flow, and resistance to changes in pipe volume.

This has come to be known as conventional current flow. Then in 1897, British physicist Thompson, discovered that current flow was really electrons as he was doing some research on a crt.

For unidirectional current flow, the REF-pin of the ZXCT181Q is tied to GND. The ZXCT18xQ series has four fixed voltage gain options—20V/V, 50V/V, 100V/V, and 200V/V.