Which instrument measures the difference in pressure between two points and can measure draft?

The instrument that measures the difference in pressure between two points and can also be used to measure draft is the manometer. A manometer operates on the principle of balancing a column of liquid against the pressure to be measured. It is commonly used in various applications, including HVAC systems and boiler operations, to assess the pressure levels and ensure proper operation.

Draft measurement is especially important in boiler operations, as it indicates the flow of flue gases and air through the system. Proper draft levels are crucial for efficient combustion and maintaining safety within the boiler system. The ability of a manometer to register pressure differentials makes it a valuable tool in monitoring and controlling systems where pressure variations are critical.

In contrast, a barometer is designed to measure atmospheric pressure and is not suitable for assessing pressure differences in a confined space or determining draft. A thermometer measures temperature, which is unrelated to pressure measurements. An altimeter, while also based on pressure measurement, specifically measures altitude by assessing the atmospheric pressure at various heights and does not serve the purpose of measuring pressure differences like a manometer does. Thus, the manometer is the correct choice for this question.