How to use a barometer

17th November 2021 Elena Manighetti

How to use a barometer

Modern technology has become so good that most boaters don’t know how to use a barometer these days.

You can easily check the marine weather forecast and look at detailed information, such as estimated wind speed and swell height, directly from your smartphone on an app like Deckee. So why should you know how to use a barometer?

Why use a barometer on a boat

There are areas in which phone signal is still unreliable, even close to the coast. Think of national parks and remote bays. Hopefully, coverage will improve in the next few years, thanks to satellite internet services. However, for now, you have to make do. Conditions can change even in just a few hours, so keeping an eye on the current trend is important.

You are also very likely to lose phone signal on longer, especially multi-day, offshore boat trips. If you’re a sailor who wants to travel long-distance, you can go for days and days without internet. Reading a barometer is easier and cheaper than getting an SSB radio qualification or buying a sat phone. Plus, technology breaks.

Bear in mind that, even though weather forecasting has become more and more accurate, Mother Nature can play some tricks. Unsettled weather can bring heavier or lighter conditions than forecast and low-pressure systems can arrive sooner than predicted.

So knowing how to use a barometer is a great backup for boaters. When the forecast models don’t agree, check your barometer for clues. When you’re offline for a day or more, keep an eye on it, just in case.

How barometers work

Before we delve into the practical side of things, let’s quickly look at how barometers work, so you can interpret one better. 

Barometers measure air pressure. This allows them to detect small changes, which are a good indication of how the weather is behaving. High-pressure systems generally bring clear, warm, and sunny days, while low-pressure systems are accompanied by water-bearing clouds and thunderstorms. A lowering in pressure signifies an incoming storm.

How to set up a barometer

Setting up a barometer is easy and quick. All you need is a small screwdriver. Make sure to follow these steps before using your instrument, so it will report accurate readings.

  1. Google the current barometric pressure for your area 

  2. On the back of the barometer, find the adjustment screw (it says “+” and “-”)

  3. Using a screwdriver, turn the screw so the movable needle displays the correct reading

  4. Match the position of the second, fixed needle to the one of the reading.

And you’re done. The barometer is set up and ready to use. 

How to use a barometer

Using a barometer is incredibly easy.

  1. Lightly tap on the screen of the instrument

  2. Watch the movable needle move up or down from the fixed needle

  3. Take a reading: rain, fair, stormy, very dry, or change.

The first time you use it, check that the reading matches the latest weather report for your area. This will tell you how accurate the barometer is.

A useful thing to know is that, typically, the average sea-level pressure is about 29.2 inches. Pressure rarely goes 1 inch above or below the 30-inch mark, unless extreme weather conditions are coming.

How to use your phone as a barometer

If you don’t have space on your boat to fit a barometer, you can use your phone. Here’s how to do it.

  1. Find the barometer and altimeter app in your utilities, or download one

  2. Tap on “set” to line up the “fixed” needle with the movable one

  3. Check back to see how the pressure is changing.

Some apps will record pressure changes and display them at the bottom of the instrument.

So, as you can see, using a barometer is easy and can be done for free, directly from your smartphone. Knowing how to read it is a useful skill that can help you understand trends in the weather when you are offline. It can be very handy when the forecast isn’t 100% accurate.

Download the Deckee app from the App Store or Google Play to stay safe on the water. Always check the detailed marine weather forecast on the app before heading out to your boat. Do not go boating if the conditions are challenging - they could deteriorate.