Samsung Galaxy Watch8 Classic (46 mm, Bluetooth) / Amazfit T-Rex 3 (48 mm)

It is sold in one size only.

Sapphire crystal is a cover material that resists scratches better than ordinary glass.

There is also a night display mode.

The rotating bezel lets you scroll lists and apps without touching the screen; its position is read by a 3D Hall sensor found only on the Classic. Quick Button can be assigned to an app or function.

Samsung says its charge times were measured with a separately sold 25 W adapter.

A full charge takes about 3 hours; a magnetic charging base is in the box but no USB-C cable. Low-temperature mode gives 28 hours with GPS on and 32 days with it off. The maximum GPS mode works only in hiking and climbing modes.

Setup and use need an Android 12 or later phone with more than 1.5 GB of memory and Google Mobile Services.

Health features are for general wellness and fitness, not medical diagnosis.

The watch offers an altitude assistant, storm alerts, compass, sunrise/sunset and tide information, and prompts for blood-oxygen readings at high altitude.

The second frequency (L5) helps accuracy where signals bounce, such as among tall buildings or under trees.

Wi-Fi is used to download software updates without the phone. The watch shows incoming calls but cannot take Bluetooth calls; quick reply works on Android only.

5ATM suits surface water use such as swimming, not diving or high-speed water sports. Samsung says its MIL-STD-810H testing cycled the watch between –20 °C and 50 °C for 6 hours in total.

The 22 mm strap is a standard width and can be swapped.

10 ATM means withstanding the pressure of 100 metres of still water for up to 10 minutes. Breath-hold training and testing are downloaded through the Zepp app.

Dual-band positioning receives two frequencies from the satellites to reduce drift from reflected signals among tall buildings and dense trees; it uses more battery. Automatic mode switches settings based on signal strength.

Chest straps, running/cycling power meters and cycling speed/cadence sensors can be paired; data can be exported to apps such as Strava, komoot and Apple Health.