The Polar M400 is a mid-range GPS watch from the company that basically brought heart rate tracking to the general public, with a long history of sports devices.

Normally retailing for £130, the Cyber Monday discount brings a healthy saving on this excellent running watch, which is decidedly affordable at £81.99 - but only for one day.

The Polar M400 is a watch designed for athletes, in this guise providing GPS data for route tracking and speed data, while heart rate data comes from the accompanying chest strap.

One of Polar's strengths - apart from being able to deliver accurate data on your training and performance - is Polar Flow. This is where Polar crunches your data and keeps track of your activity.

One of the things we really like about Polar's devices is that they are approachable: Polar Flow lets you see what your workout did for your fitness, so you're not just looking a numbers and graphs.

The M400 has now been superseded by the M430 (which adds wrist-based heart rate tracking), but that's going to cost you more.

But, Amazon is also discounting a range of other Polar devices for Cyber Monday, so it's worth having a browse and seeing what fits your requirements. This is a limited time offer, however, so choose quickly.