A barometer measures atmospheric pressure, which helps predict short-term weather changes. Rising or falling pressure can indicate improving weather, approaching storms, or changing conditions.
Mechanical barometers are widely used in homes, boats, and weather stations because they provide a reliable way to monitor weather patterns without electronics.
This guide explains how to read a barometer correctly and how to interpret what the changes in pressure mean.
A barometer measures barometric pressure, which is the weight of the air in the atmosphere pressing down on the Earth.
Pressure is usually measured in:
Hectopascals (hPa)
Millibars (mb)
Inches of Mercury (inHg)
Most modern mechanical barometers in Australia and New Zealand display pressure in hPa, where the average sea-level pressure is around 1013 hPa.
Most traditional barometers have two indicators:
1. The Moving Needle
This shows the current atmospheric pressure.
2. The Reference Needle (Set Marker)
This adjustable needle allows you to mark the previous pressure reading so you can easily see if pressure is rising or falling.
Watching the direction of pressure change is more important than the exact number.
When you first install a mechanical barometer, it may need to be set to match the local atmospheric pressure.
Steps:
Find the current pressure for your location (from a weather website or weather station).
Use the adjustment screw on the back of the barometer.
Turn the screw slowly until the needle matches the local pressure reading.
Once set, the barometer will track pressure changes automatically.
The most important thing is whether pressure is rising, steady, or falling.
Rising Pressure
Improving weather
Clearing skies
Stable conditions
Steady Pressure
Little change in weather
Stable atmosphere
Falling Pressure
Approaching rain or storm
Increasing wind
Unsettled weather
A rapid drop in pressure often indicates a strong weather system approaching.
| Pressure (hPa) | Weather Trend |
|---|---|
| 1025+ | Very stable, clear weather |
| 1013 | Average pressure |
| 1005 | Unsettled conditions |
| 995 or lower | Stormy weather likely |
These ranges can vary depending on location and season.
Many people assume the number itself predicts weather, but experienced users watch the trend over time.
For example:
1015 dropping quickly → rain likely
1005 rising steadily → weather improving
Tracking the pressure change over 12–24 hours gives a much better forecast.
Mechanical barometers work indoors and are not affected by indoor temperature.
Best placement:
On an interior wall
Away from direct sunlight
Not near heaters or air vents
They work equally well in homes, offices, and boats.
High-quality mechanical barometers are surprisingly accurate and can track pressure changes very reliably.
Many professional instruments are still made using traditional aneroid capsule technology, which expands or contracts as air pressure changes.
Well-made barometers can last many decades with minimal maintenance.
A barometer is one of the simplest and most fascinating instruments for understanding the weather.
By watching how atmospheric pressure changes throughout the day, you can often predict weather patterns before they appear in forecasts.
Whether used at home, on a boat, or in a workshop, a well-made barometer provides a reliable and timeless way to stay connected with the changing atmosphere.