(Image credit: Future) I ran my sixth marathon last weekend — the 2026 London Marathon, and, ever the tech tester, I decided to strap two watches to my wrist for the experience. Sure, it raised some questions on the start line, but the London Marathon is a great test of how well watches really cope with crowds, skyscrapers, and 26.2 miles of recording data. For the run, I wore the Apple Watch Ultra 3 and the Garmin Forerunner 570 . Both watches have bright, beautiful displays and dual-band GPS, designed to boost tracking even in challenging environments. Article continues below That said, the point of this test was to look at how well Apple versus Garmin performed over the run. The London Marathon is notorious for being a GPS dead spot, and is conveniently positioned between miles 19-21 of the London Marathon — a time where you really don’t need GPS mind games. Below, I’ve crunched the data and compared the usability of the watches over my run. Read on to find out more.…