If you are serious about your training, you may want to invest in a sport watch. The Garmin Forerunner 955 is waterproof and has plenty of useful features.
From Amazon
Garmin Forerunner 955 3,3 cm (1.3") LCD Numérique 260 x 260 pixels Écran tactile Noir Wifi GPS (satellite)
RunningXpert
Garmin Forerunner® 955 Black ONESIZE
This product is also available at 4 unverified merchants.
Too expensive? Get a notification as soon as the price drops.