How to read a barometer?

How to Read a Metric Barometer

• Answer:

  Barometers measure pressure in the atmosphere. The pressure fluctuates daily and can help determine short-term weather conditions. Because pressure is measured in at least a dozen different units and standards, you might come across a barometer with output readings that are in metric units instead of English units. Converting to a more familiar unit of pressure is simple if you know the conversion factors. Difficulty: Moderate Things You'll Need Calculator Instructions Check the metric barometer's reading. Give the device a small tap with your finger, and wait a few minutes to let it settle. This ensures your reading is accurate and makes sense. Pressures are typically lower than average in cloudy weather and higher in clear and dry weather. Record the metric reading. The metric unit for pressure is the Pascal (Pa), and it is a measure of force per unit area with dimensions of kilograms / (meter x seconds^2). One atmosphere is equivalent to 101325 Pa. It is common to report metric pressure in kiloPascal (kPa); in that format, 1 atmosphere = 101.325 kPa. Convert the metric reading to Pascal if it is in kiloPascal by multiplying it by 1,000. Divide the result by 101325 to get the pressure in atmospheres (atm). One atm is equivalent to 14.7 pounds of pressure per square inch (psi). If the barometer read 180 kPa, for example, then 180 kPa x 1000 = 180000 Pa. Also, 180000 Pa / 101325 Pa per atmosphere = 1.77 atm. That is 25 psi because 1.77 atm x 14.7 psi / atm = 25 psi. Compare your answer to the standard pressure at sea level, which is 14.7 psi. Pressure varies with temperature and altitude, but most barometers are designed to account for those factors in their reading.