A diaphragm type pressure gauge:

A diaphragm type pressure gauge is designed to measure pressure through the deflection of a flexible diaphragm. This mechanism is particularly effective for measuring low pressures and small pressure changes. When external pressure is applied to one side of the diaphragm, it deflects, and this movement is then translated into a pressure reading.

This design makes diaphragm gauges highly sensitive and ideal for applications that require monitoring fine variations in pressure, making the statement about their ability to measure very small pressures accurate. In contrast, while diaphragm gauges can be used for pressures close to atmospheric levels, they are not primarily intended for high pressures, which is why the option regarding the measurement of high pressures is not correct. Additionally, the operation based on a mercury column pertains more to traditional manometers rather than diaphragm gauges, aligning with the incorrect associations present in the other options.