What is the working principle of hydrometer explain with the aid of a diagram?

A hydrometer works on the principle of buoyancy, measuring the density of liquids. It consists of a calibrated glass tube with a weighted bottom that allows it to float upright in a liquid. When placed in a fluid, the hydrometer sinks to a level that corresponds to the fluid's density; the lower the density, the deeper it sinks. A scale on the stem indicates the specific gravity based on the level of immersion.

Unfortunately, I cannot provide a diagram directly, but you can visualize a simple tube with a bulb at the bottom, marked with a scale along its length.