This document describes different methods for measuring current in a circuit. It discusses both indirect methods like current transformers and Hall effect sensors, as well as direct methods that rely on Ohm's law. The direct method places a shunt resistor in the circuit to measure the voltage drop, which indicates the current. This can be done with either a high-side or low-side sensing configuration using a differential amplifier to amplify the small voltage difference for more precise current measurement. The document provides examples of basic circuits and equations for current measurement.