A lighter watch is more comfortable to wear all day.

The case diameter; larger cases fit bigger displays, smaller ones suit slimmer wrists.

The case material (e.g. aluminium, titanium).

A higher ATM rating allows swimming and diving.

Shows the time and stats without raising your wrist.

A scratch-resistant sapphire crystal protects the screen.

A larger display is easier to read and interact with.

A higher pixel count produces sharper text and graphics.

The screen technology (e.g. AMOLED).

A brighter screen is easier to read in sunlight.

Continuously tracks your heart rate.

Measures blood-oxygen saturation.

Takes an electrocardiogram to check heart rhythm.

Estimates blood pressure from the wrist.

Monitors sleep stages and quality.

Tracks routes and distance without a phone.

Estimated hours of use between charges.

Tops up quickly from empty.

Charges on a wireless pad or puck.

How long a full charge takes; lower is better.

A newer Bluetooth version improves range and efficiency.

Connects to Wi-Fi for updates and sync without a phone.

L1+L5 GPS gives more accurate tracking in cities and forests.

Make calls and stream without your phone nearby.

Pay contactlessly from your wrist.

Take calls and use a voice assistant on the watch.

The watch software platform.

More storage holds more offline music and apps.