Apple Watch Ultra 2 review: specs and price

The size of the screen (measured diagonally).

The type of technology used in the display.

The device is dustproof and water-resistant. Water-resistant devices can resist the penetration of water, such as powerful water jets, but not being submerged into water.

The ATM rating indicates how much water pressure a device can withstand. 3 ATM is one of the lowest ratings and means that the device can only withstand splashes of water, whereas 20 ATM is one of the highest ratings and means that the device can be used for snorkeling and water sports.

The first number of the IP rating refers to protection against dust, while the second number refers to protection against liquid. E.g. a first number of 6 denotes that it is completely dustproof, and a second number of 7 denotes that the device can withstand full immersion in water.

Damage-resistant glass (such as Corning Gorilla Glass or Asahi Dragontrail Glass) is thin, lightweight, and can withstand high levels of force.

Gorilla Glass is one of the most popular brands of chemically strengthened glass, manufactured by Corning. Several versions have been developed, the newer ones being more durable and providing better damage resistance.

Pixel density is a measurement of a screen's resolution, expressed as the number of pixels per inch (PPI) on the screen. A higher pixel density translates into more clarity and sharpness for the images rendered on the screen, thus improving the quality of the viewing experience.

Resistance to sweat makes it ideal for use while doing sports.

Your blood oxygen level is a measurement how much oxygen is reaching your muscles. It is important because low levels mean that you will become easily fatigued during exercise. The more exercise you do, the better your blood oxygen levels will become.

A heart rate monitor can help show your fitness levels, enabling you to calculate a suitable intensity of exercise.

GPS enables global positioning, useful in map, geo-tagging or navigation apps.

An accelerometer is a sensor used to measure the linear acceleration of a device. A common application is detecting when a device changes between vertical and horizontal positions.

With a temperature sensor you can monitor changes in temperature to measure your exertion levels and avoid hyperthermia.

A compass is useful for gaming, maps, and navigation software.

This measures barometric air pressure. It can predict weather changes, for example a sudden drop in air pressure could mean a storm is coming. When calibrated correctly it can be used to determine altitude, which helps GPS devices to lock on quicker and with greater accuracy.

A gyroscope is a sensor that tracks the orientation of a device, more specifically by measuring the angular rotational velocity. Initially, they were built using a spinning rotor to detect changes in orientation, like twisting or rotation.

A cadence sensor measures the number of pedal revolutions per minute when you are cycling. It enables you to monitor how fast you are pedaling.

It can track your sleep, such as how long you sleep for and the quality.

It tracks how far you travel.

It tracks how many steps you take throughout the day, allowing you to see how active you have been.

Measuring pace shows how much time it takes to travel one kilometer or one mile. For example, in running, a 4 minute kilometer would be a very good pace.

Your sleep data is analysed to give you a report, available to view through the app or website. This allows you to see the quality of your sleep and to help you make improvements.

The device automatically detects when you start an activity such as jogging, saving you from entering it manually at a later time.

With a route tracker you can add your route onto a map. It is helpful if you plan to do the same route again, or want to share it with your community.

It can detect changes in elevation, such as when you are climbing stairs.

A multi-sport mode allows you to easily switch between tracking different sports such as running, cycling, and swimming. This feature is ideal for those who need to change quickly between various activities (e.g., triathletes).

It is compatible with a range of iOS devices such as iPhones, iPads and the iPod Touch.

It is compatible with a range of Android devices such as smartphones and tablets.

Bluetooth is a wireless technology standard that allows data transfers between devices placed in close proximity, using short-wavelength, ultra-high frequency radio waves. Newer versions provide faster data transfers.

The device can connect to Wi-Fi.

The Wi-Fi versions supported by the device.

ANT+ is a wireless protocol similar to Bluetooth Smart, and is very power efficient. It is mainly used for fitness monitoring devices such as heart rate monitors and cadence sensors to connect to other devices (e.g., sports watches, smartphones, and cycling computers).

The number and type of SIM cards supported.

NFC (near-field communication) allows a device to perform simple wireless transactions, such as mobile payments. Note: this feature may not be available in all markets.

Devices that use cellular technology can connect to mobile networks. Cellular networks have much wider signal coverage than Wi-Fi.

With a longer battery life, you don’t have to worry about charging the device as often.

Battery power, or battery capacity, represents the amount of electrical energy that a battery can store. More battery power can be an indication of longer battery life.

With a long battery life, you can train for several hours a week and only have to recharge the device every few weeks.

The time it takes to fully charge the battery.

In power save mode you can still check what time it is and other basic functions. A long battery life is good if you wear the device day to day.

There is less chance that you will run out of battery during an adventure.

It supports a wireless charging standard such as Qi. To charge the device, you simply put it down on a compatible charging pad.

The battery can be recharged and used over again.

A solar battery takes its energy from light, and stores it in a self-recharging battery which never needs to be changed.

Heart rate variability (HRV) tracking measures fluctuations in the time between heart beats. These fluctuations can be an indication of health conditions (such as heart conditions or mental health issues). Note: This feature may not be available in all markets.

VO2 max capacity is a measurement of the amount of oxygen your body can use during physical exercise. A high VO2 max capacity indicates good fitness levels.

This measurement is your heart rate per minute when you're at rest, such as when you're relaxed, sitting, or lying down. For adults, this is typically between 60–100.

It can notify you when your resting heart rate is above or below the normal range.

This is based on various information, such as your previous workout, sleep quality, and stress levels. Taking everything into account, it will give you an idea of whether your body is ready for another workout or if you should focus on recovery.

The device has a speaker and microphone that allow you to answer calls made to your smartphone.

The device has a feature that allows you to find your smartphone if you have misplaced it.

The device alerts you to incoming calls on your smartphone, and allows you extra control such as muting or rejecting the call.

If you get a notification such as a call or message, the device will vibrate on your wrist or make a noise to alert you.

Your activity data is analysed to give you reports, available to view through the app or website. This allows you to see how active you have been and to help you make improvements.

The device detects when you have been idle for too long, and alerts you to encourage you to stay active.

This is useful if you are on a strict training diet or if you are trying to lose weight. It can also help to boost your motivation.

Allows you to set your own goals, such as reaching 15,000 steps in a single day.

You are awarded achievements for reaching goals, helping to encourage you and keep you motivated.

You can download the app for free, from platforms such as Google Play or the App Store.

It has an exercise diary, allowing you to easily keep track of your previous workouts.

Adverts can be distracting and obtrusive. Apps and blogs without ads are more aesthetically pleasing, nicer to use, and make the content stand out.

The app can determine the best way for you to progress in your exercise, and offers coaching advice.

An indicator shows you when the device has low battery.

aptX is a codec used for transmitting audio wirelessly with Bluetooth. It is developed by Qualcomm, and supports 16-bit audio at a bit rate of 384kbps.

It can determine when you have stopped working out and pause your current workout tracking until you start moving again.

You can set a passcode to keep your data private.

It is compatible with smart scales such as the Fitbit Aria and Withings range. These scales transmit information such as weight and BMI to connected services over Wi-Fi.

It supports third-party heart rate monitors to incorporate your pulse data.

It is compatible with PCs and laptops running the Windows operating system.

The device has a standard memory slot (such as an SD or micro SD card slot) that enables you to extend the built-in internal storage with affordable memory modules, or easily retrieve data, such as photographs, from the memory card.

With a standard mini jack socket, you can use the device with most headphones.