Welcome to Alti-Barometer!

Alti-Barometer uses your iPhone’s or Watch’s barometric pressure sensor to detect weather changes or show your altitude. Alti-Barometer can run independently in your iPhone, Apple Watch, or in combination. It supports all Watch complication styles, and also supports iOS 14 widgets. The app will display a continuous 24-hour log of altitude and barometric pressure, and allows you to graphically explore altitude and barometric trends and data.

Getting started

There are many factors that can affect pressure sensor readings and their interpretation, and that this app is exclusively for recreational and entertainment use only.  It is not intended for navigation or any situation where use of the app could compromise safety.


Alti-Barometer will display barometric or altitude-related information based on your preferences and allows you to easily switch between the two modes on the fly. It also has an automatic mode that will display the most appropriate information based on your activity.


Changes in altitude and weather changes both impact air pressure. Even a small change of a few dozen feet in elevation will be the equivalent of a meaningful change in terms of weather-related barometric pressure, and weather-related pressure changes will have the same impact on air pressure as a change in altitude. To mitigate the inherent challenges with measuring and interpreting air pressure-related data, Alti-Barometer provides a combination of advanced features including GPS assist, intelligent filtering of altitude changes, and auto-switching between altimeter and barometer modes based on your activity.


The app requires location services to be enabled to obtain barometric pressure data and to be able to access GPS location data needed to determine an altitude reference point required for accurate pressure-based readings.


When installing the app, accept the request to always use your location; this is required for the app to function. Per the app’s privacy statement here, your location information will only be used to enable the app’s operation, and will not be shared or made available outside the app in any way.

Watch sync mode


Both the iPhone and Watch apps can operate completely independently of each other. In addition, the iPhone and Watch versions of Alti-Barometer can operate together, with the iPhone app feeding barometric pressure and altitude updates for the synced Watch app to display . One advantage of synced operation is that the same information will be displayed on both devices. Also, the use of the iPhone’s pressure sensor will typically provide more accurate results, and Watch battery life will also be increased by offloading computation to the iPhone’s more powerful hardware.


The default mode is synced operation. You can turn the sync feature on and off by tapping the “Watch sync” button on the iPhone app. When turned off, the Watch’s interface will switch to standalone mode which will allow you to run the app independently. If your iPhone is not in range of your Watch or you chose to remove the app on your iPhone, the Watch’s interface will automatically switch to stand-alone operation.


The “Watch sync” button on your iPhone will indicate whether the sync feature is enabled and if you have a Watch paired to your phone, whether your Watch is in range:

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Phone actively syncing the Watch

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Phone sync on with Watch not detected

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Phone sync off with Watch detected

For optimal Watch battery life, the default sync mode is "Eco sync" enabled. With Eco sync on, the Watch will be updated every 10-15 minutes with new data to maximize battery life. This is especially ideal if you are primarily interested in tracking barometric pressure which changes slowly over time. Eco sync mode will still display altitude data, but if may not display the most current data. If you want to see the very latest altitude information on your Watch when running with Eco sync enabled, tap on the Alti-Barometer complication on your Watch face to open the app and see the current altitude. When you close the Watch app, it will continue to report real-time altitude data on your Watch face for a minimum of five minutes, or until the app senses that you are no longer actively climbing or descending.

If you turn Eco sync off, your Watch face will continuously display real-time barometric and altitude data supplied by your iPhone. After you turn Eco sync off, you will need to open the Watch app to activate continuous reporting. Note that real-time reporting on your Watch face will decrease your battery life.

Interface Controls


Alti-Barometer uses custom controls that are designed to work as similarly as possible between the iPhone and Watch versions of the app.


Option selection buttons allow you to select one of multiple options such as the graph style or operation mode. To select an option with this type of control, tap the desired option button to activate it. The button will be highlighted, and will display the currently selected option for the button as well as the type of option being changed. With the button active, slide your finger up or down to scroll to the desired value displayed inside the button at the bottom inside the green outline. If your finger obstructs your view of the option displayed in the button, you can slide your finger to either side of the button, and then slide your finger up or down to select the desired option. On the Watch, rotating the digital crown while an option button is active provides an alternative way for you to scroll through available options.

Slider-style buttons allow you to select a numerical value such as reference altitude. To use this type of control, first tap the button. This will activate the button and enable it to be changed. When enabled, the button will be highlighted and will display “+” and “-“ symbols on either side of the button. You can either tap the plus/minus symbols to increment or decrement the button value, or you can hold your finger down to continuously adjust the value in the desired direction. You can also drag the orange slider circle to adjust the desired value up or down more quickly. Once you have taken your finger off the button for a few seconds, the button will revert to its unactivated state. On the Watch, rotating the Digital Crown while the button is enabled will also allow you to increment or decrement the selected value and can be much easier than trying to use your finger on the small watch display.

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Option button in active selection state

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Value slider button in active state ready to change the selected value

Basic operation


When launched, the app will automatically start running on the iPhone, and the Watch will automatically start in sync mode. 


The iPhone app has three screens: the main screen, a “Stats” screen displaying key statistics, and a "More options” screen to access options such as calibration settings.


The Watch app has two screens in synced mode, or 4-5 screens when running independently. In synced mode, the Watch will display a “Phone widget” screen displaying a graph of either barometric pressure or altitude depending on the current mode, and an app information screen. When running independently, the Watch app will display multiple screens to allow selection and adjustment of the same options as are provided on the iPhone app as well as a separate screen displaying the  interactive graph of barometric pressure or altitude. The interactive graph on the Watch has the same features as functionality as the graph on the iPhone.  Navigation between the Watch app screens can be accomplished by swiping left and right. Note that the swipe on the graph screen needs to be on the bottom portion of the screen since the area used to display the graph is used to interact with the graph.


Watch Complications


Alti-Barometer supports all available Watch complication styles and has been designed to convey as much glanceable information as possible.  The two large Watch complication styles provide a graphical display of barometer and altimeter trends similar to what is displayed by the widget and interactive graph screens, and they are very effective in spotting barometric or altitude trends at a glance on your wrist. The non-graphical complications provide glanceable trend information as well using trend directional and other data. In barometer mode, directional arrows indicate pressure trends over the past two hours, a forecast icon and/or message is provided based on the current barometric pressure, and the latest pressure value is also displayed.  In altimeter mode, the complication displays current altitude, and trend arrows show the altitude trend over the past minute with each arrow representing the past 30 seconds. If the calculated climb rate is greater than the vertical speed threshold specified in the VSI setting, the altitude complication will display vertical speed and direction with an upwards arrow indicating ascent, and a downwards arrow indicating descent. In complications with sufficient display area, the altitude complication will also display an estimate of oxygen availability based on altitude. 8,000’ feet is used as the reference point where some people may feel ill due to lack of oxygen, and 26,247 feet corresponds to Mt. Everest’s “death zone”. Note that altitude-based oxygen information is for reference only and is not to be used for determining altitude-based oxygen levels.


While all the complications provide useful at-a-glance information, the large graphic complication provides the richest amount of data and is recommended for the optimal Alti-Barometer Watch experience.


Large graphic along with small circular complication.

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Extra large complication style with real-time altimeter activated..

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Storm alarm

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Utilitarian styles




The app enables accurate calibration of the device’s barometric pressure sensor hardware. This allows the app to adjust for sensor inconsistencies that vary from one device to another. Calibration allows compensating for such inconsistencies by using accurate values for your altitude above sea level, and barometric pressure at your location using a high-quality reference reference. You can obtain your current altitude by using the “Get GPS ref” button in then app, or by using any number of other apps including Apple’s build-in Compass app. You can get the barometric pressure at your location using a weather app such as weather.com or wunderground.com.

Once you’ve set an accurate reference altitude using the "Ref" adjustment button, use the “Baro cal” button to adjust the displayed barometric pressure value up or down until it matches the current validated barometric pressure at your location. The amount of calibration adjustment will be displayed in the square "[ ]" brackets. Once this process is complete, the adjustment value will be added to all future values of the hardware pressure sensor’s "raw" value to obtain the corrected pressure sensor (e.g. station pressure) value.

Note that you only need to do this once; the app will save the adjustment value, and the calibration value typically does not change over time. Be aware that temperature can impact pressure sensor values. If you intend to use the Watch app independently, you should perform calibration after having worn the Watch for 10-15 minutes to allow it to warm up to your body temperature.

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Before calibration: Reference altitude verified, local weather station reporting 30.05 inHg

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After calibration: Alti-Barometer barometric pressure and reference weather station value match with a calibration adjustment of 0.05 inHg

Graph display and navigation


The interactive graph on the iPhone and the Watch (when running independently) allows you to explore the barometric and altitude data the app has collected. The graph supports three types of gestures:  tap, tap-hold-drag, and swipe. As with the interface controls, the gestures were designed to operate the same way on the iPhone and Watch versions of the app:


When you are zoomed into the graph, the swipe gesture will allow you to scroll the graph to the left or right.


A single tap gesture will activate a vertical orange cursor at the approximate tap location. When the orange cursor is displayed, the data value corresponding to the cursor location will be displayed directly under the graph.


The tap-hold-drag gesture allows you to drag the cursor to the desired location on the screen to show the exact data value you're interested in seeing.


On the Watch, you can also use the Digital Crown to easily change the location of the cursor when it on screen.


Due to space limitations, controlling zooming into the graph works differently on iPhone and Watch versions. On the iPhone app, use the slider below the graph display to select the desired horizontal scale represented as a time interval. On the Watch, you can zoom in or out of the graph using Digital Crown when the cursor is off.

On both versions of the app, the yellow zoom/scroll indicator directly under the graph provides a visual reference for what portion of the data you are currently viewing (the position of the yellow indicator bar), and how much of the total available data you are viewing (the width of the yellow indicator bar).


Note that whenever you activate and display the app on either the Watch or iPhone, the graph screen will initially display the full range of the data the app has collected so far.

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Example of cursor active in barometer mode examining data recorded at 11:56 am along with the reference altitude used to calculate the barometric pressure.

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Example of data cursor in altimeter mode. The "⇅" symbol indicates an climb or descent event at the location being examined.


Individual features


Altimeter/Barometer selection


Selecting the “Altimeter” or “Barometer” feature on the main screen will switch the functioning of the app to the desired setting. Note that if the “Auto” operation mode has been selected, the app will automatically switch from altimeter to barometer when it has detected a stable altitude appropriate for barometric operation for at least five minutes.


Graph style


The graph style button will display the currently selected graph style. Tapping this button will allow you to choose one of three graph styles: a dot graph, and bar graph, or a smooth line graph. Note that complications and widgets always display a smooth line style graph since it is best suited to small display areas.


Graphs are color-coded to indicate trends. In barometer mode, a red shading indicates dropping barometric pressure and green indicates rising barometric pressure; the color intensity corresponding to the intensity of the change. Altimeter mode uses a similar scheme and uses the VSI setting to determine the color intensity with the graph color becoming more intense as the measured vertical speed approaches the VSI threshold value.


Units selection


Alti-Barometer supports hectopascal, inches, and millibar units for barometric pressure, and feet and meters for altitude and vertical speed. The default is inches of mercury for pressure, and feet for altitude. To change the desired setting, select Altimeter” or “Barometer”, and then use the “Units” button to select the unit to use for the desired measurement. Note that vertical speed will be shown as feet per minute, or meters per second.




The “Scale” adjustment allows you to set the minimum scale value for the active mode (“Altimeter” or “Barometer”). Graphs of barometric pressure and altitude will attempt to use the selected scale value to display the appropriate data. If the range of the collected data is greater than when can be displayed using the selected “Scale” value, the app will automatically use smallest scale value that will accommodate displaying the full range of the collected data. In other words, the app will always auto-range the vertical scale to be able to display the full range of the data collected, and the minimum scale value setting is purely a matter of personal preference for how you would like to see the graphs displayed. A smaller setting will allow you to better visualize small changes in altitude or barometric pressure, but the scale value used will change more frequently as the range of data increases over time. A larger setting will mean fewer or even no changes to scale used to display the data over time, but smaller changes in the data will be harder to see.


Watch sync


As discussed earlier, this setting allows the iPhone and Watch to work together with the Watch serving as an extension of Alti-Barometer app on the iPhone. The Watch will display the same complications as it would running independently. Instead of an interactive graph of the data, the data display on the Watch app will mirror the widget graph on the phone and will not be interactive in paired mode. You may turn “Watch sync” mode on or off at any time, and you will see the Alti-Barometer complications and user interface on the Watch app change in response to the selected mode of sync operation.


Storm alarm


When the “Storm alarm” option is enabled, the app will monitor the barometric pressure over the past three hours and set an alarm if the barometric pressure drop over that time is greater than 4 hPa (approximately 0.12 inches of mercury), or a rise greater than 6 hPa (about 0.18 inHg). Alti-Barometer will send a notification, and will also set a notification badge on the Altitude-Barometer icon on the phone. Notifications must be enabled in the Alti-Barometer app and in system settings (Settings/Notifications/Alti-Barometer) for the the Storm notification feature to function. The storm alarm will also be displayed in the Watch complications using a “⚡️” symbol to denote a storm condition with a large drop in pressure with potential precipitation, and a "💨" symbol to indicate a large rise in pressure and potential high wind. Note that while Alti-Barometer’s algorithms will attempt to prevent false positives, changes in altitude - and the resulting change in barometric pressure - may be detected as a storm condition. A significant drop or rise in barometric pressure does not always indicate that storm conditions are developing.

You can change the length of time user to trigger a storm condition with the "Storm time" setting on the Options screen. The default is 3 hours, and you can decrease the measurement time to detect shorter bursts of barometric pressure rise or drop.



The VSI setting gives you control over the display of vertical speed in the app. When the app detects a vertical speed greater than the VSI setting, the complications as well as the status area under the live graph will display calculated vertical speed instead of altitude. If you don’t wish to see vertical speed, simply adjust VSI to a sufficiently high value. The reported vertical speed lags a few second behind actual vertical speed due to the reporting rate of the barometric pressure sensor.


Baro calibration


Refer to the calibration discussion above.


Auto GPS and GPS reference


As noted in the “Getting Started” section, all barometers need to know the barometer’s height above sea level to be able to calculate accurate readings. Relatedly, all pressure-based altimeters need to be adjusted to current sea-level barometric pressure to calculate altitude above sea level. If you know your current sea level altitude or sea level adjusted barometric pressure, you can use the “Ref” button to manually set Alti-Barometer’s reference values. Alternatively, you can use your iPhone’s or Watch’s GPS capabilities to obtain your current altitude, and will use that value to adjust the app’s altimeter and barometer reference settings. It may seem a bit strange to have to obtain your altitude to then be able to then accurately calculate your altitude, but that’s the funny nature of barometric pressure, and is the reason that even with all of today’s technology, pilots still have to constantly adjust their altimeters with barometric reference values to ensure accurate altitude readings at their destinations.


Alti-Barometer supports both automatic and manual use of GPS to establish accurate reference values. You can use the “Get GPS ref” button at any time to turn on the GPS hardware, get a fix, and have the app automatically use the resulting altitude value as a new reference.


You can also turn on the “Auto GPS” option. When the app’s operational mode is set to “Auto”, this option will automatically attempt a GPS-based recalibration when the app’s algorithms have detected a certain amount accumulated barometric pressure due to changes in altitude. If Auto GPS is on, the app will also attempt to get a new GPS-based reference value whenever it is started or re-started.


The best mode for you depends on your usage. Keep in mind that the GPS hardware uses a significant amount of power, and the most battery-friendly approach is to use GPS as little as possible, or not at all.


Obtaining a GPS-based reference may take a few minutes to locate the GPS satellites and to obtain high-accuracy data.


Reference altitude


As discussed above, accurate readings require an accurate reference altitude or sea-level pressure. This button allows you to set a manual reference for the app using the current units for altitude and barometric pressure. You can use either a known altitude or sea-level barometric pressure as your reference value.


In previous versions of Alti-Barometer, this feature was embedded as part of “Auto” mode and was used to differentiate between altitude- and weather-related pressure changes to mitigate the classic problem of altitude/barometer-capable watches: barometric pressure readings that go completely off track altitude changes, and the altimeter creeping up or down due to barometric pressure changes even though your altitude hasn't changed. We’ve been working on improving improving our unique and proprietary auto-adjustment algorithms and is sophisticated enough to use in either auto or manual modes. We recommend that you use Alti-Barometer with BaroTrak enabled.


Clearing current data


The “Clear data” button will clear the data that has been recorded. This will also reset the statics on the “Stats” screen.




The “Stats” screen will display data that may be useful including the raw air pressure value reported by the device's hardware sensor, minimum and maximum recorded barometric pressure and altitude, total accumulated climb and descent, total time spent climbing and descending, and the total run time since the recorded data has been reset of the app restarted as well as the number of GPS activations. The total accumulated climb and descent will approximations due to the fact that changing weather-related barometric pressure changes will be interpreted as altitude changes, and false positives due to inherent sensor noise.


Stats cal be reset using the “Reset stats” button on the Stats screen.  This can be handy when you want to start tracking new stats (for example, maximum altitude hiking over that next ridge) but don’t want to reset the data log of your entire hike.


Operational Notes

Hardware Requirements


This app requires an Apple Watch Series 3 or later, or iPhone 6 or later.  Previous versions of the Watch and iPhone do not include the necessary barometric pressure sensor in their hardware needed for the app to function.

Navigation icon on the Watch


If you have Alti-Barometer installed on the Watch, you will see a small white navigation icon on the main Watch screen. This  icon is not under Alti-Barometer’s control and will be displayed by WatchOS for any app that uses location services. Apps can specify any one of a variety of use categories for location services. Unfortunately, all of the available options are treated as “navigation”. As previously noted, Alti-Barometer relies on location services to work and will cause the operating system to display the navigation icon. We will keep looking for a technical solution or alternatives to this side-effect of WatchOS behavior and will monitor changes to WatchOS that may give apps more control over this behavior.

Forecast parameters


The app uses the following values (shown here using inHg units) to calculate the forecast:


pressure < 29.0575   : Stormy

pressure < 29.4709   : Rainy

pressure < 29.8843   : Change

pressure < 30.2978   : Fair

pressure >= 30.2978 : Dry

Battery life

This app has focused on conserving battery life as a core principle.  It makes minimal use of GPS hardware with as little background processing as possible, and only updates the complications when necessary to maintain functionality and usability.

Please refer to the Eco sync feature help you find the right sync mode setting for your needs.


Watch charging behavior


The Watch version of the app does not record altitude readings while running in stand-along mode and running on the charger.  This is due to a quirk with how the Apple's WatchOS software for the pressure sensor works, specifically, the pressure sensor APIs stop sending updates to the app when the Watch is on the charger.

When on the charger, the Data graph screen will display “Paused…” in the data area at the bottom of the screen to indicate that it isn’t able to collect new data while connected to the charger. When you remove the watch from the charger, it will pick up where it left off. If the app is running on the iPhone and is within range of the Watch, the app on the Watch will use the iPhone's pressure data as a substitute while on the charger. If data from the phone is not available, the app will interpolate the missing data, and will denote that the missing data has been artificially “filled in” by using a purple color on the data graph screens. This limitation will be addressed if the operating system behavior changes in a future WatchOS update.