Which of the following is not considered a pressure measuring device?

A hygrometer is a device used to measure the humidity or moisture content in the air, rather than measuring pressure. It functions based on various principles, such as the absorption of moisture in a material or variations in electrical resistance due to humidity changes. The other options all specifically measure pressure.

Barometers measure atmospheric pressure, typically used in weather forecasting, while manometers measure the pressure of gases or liquids within a system. Pressure transducers convert pressure measurements into electrical signals that can be interpreted or processed. This clear distinction highlights why the hygrometer does not fit into the category of pressure measuring devices.