>Yes, runners can use a variety of electronic devices (GPS watches, heart rate monitors, accelerometers on your shoe) to try to set their own pace but none of these are perfect. They also require constant attention.

Yes, those devices do require constant attention, usually by glancing at watch, what is rather distracting. But, something that mostly resolved this deficiency, at least for me, was Garmin Varia Vision - tiny heads up display mounted to sunglasses. it can keep in your eyesight all the relevant metrics. It is a great help for me in outdoor runs