Here's a breakdown of how and what it can measure:

* How it works: A galvanometer uses the principle of electromagnetism. A small coil of wire is placed within a magnetic field. When current flows through the coil, it experiences a force that causes it to rotate. The amount of rotation is proportional to the current flowing through the coil.

* What it measures:

* Direct Current (DC): This is the most common type of current measured by galvanometers.

* Small Currents: Galvanometers are particularly sensitive and can measure very small currents.

* Current Direction: A galvanometer can indicate the direction of current flow, as the coil rotates in one direction for positive current and the opposite direction for negative current.

However, it's important to note that:

* Modern Applications: While historically galvanometers were widely used, they have largely been replaced by digital multimeters for most practical current measurements.

* Limitations: Galvanometers are not used for measuring alternating current (AC) directly. They are also generally not suitable for measuring very high currents.

In summary, while the galvanometer is a fundamental instrument for understanding and measuring electricity, it's primarily used for detecting and measuring small DC currents.