Which device is typically used to measure flow?

The device that is typically used to measure flow is a flowmeter. A flowmeter is specifically designed for measuring the flow rate of liquids and gases. It operates by assessing various factors such as pressure, velocity, or volume to provide accurate readings of the flow within a system. Flowmeters come in various types, including mechanical and electronic, and can be used in numerous applications, from residential plumbing to large industrial systems.

In contrast, while a weir can also be involved in flow measurement, it is primarily used to create a specific head of water that can then be correlated to flow rates using established formulas. It does not directly measure flow but rather allows for flow measurement based on the height of the water over the weir.

A hydrometer measures the specific gravity of liquids, which is not a flow measurement. This instrument is used primarily in tasks like determining the concentration of solutions, rather than quantifying the flow rate.

A barometer measures atmospheric pressure and has no application in measuring flow rates of liquids or gases, making it unrelated to the question of flow measurement.

Thus, the correct choice for measuring flow is clearly a flowmeter, as it is specifically engineered for this purpose.