Found on Competitor.com and written by Sam Winembaum
A few tips and tricks regarding your GPS watch and heart rate monitor that you may not have known:
GPS run distance is now very accurate. We have noticed minimal distance differences between simultaneously running GPS watches or phones, at least on the open road. They are all very accurate these days, and most when connected to app or computer, now update current GPS signal satellite locations. Yes, their orbits do change. Up-to-date satellite location information is key to acquiring as many satellites as possible to fine-tune GPS accuracy. With fewer satellites in the mix your captured path may drift from actual. While your GPS may say you are good to go, give it a few minutes to acquire as many satellites as possible, orienting yourself with an open view to the South sky.
Trail running can result in less accurate GPS distances, usually shorter than actual, due to many turns not completely caught between GPS sample points and obstruction of the satellite signal by terrain features. Some of the same issues can apply when running in cities with tall buildings.
Race courses are measured on the shortest tangents, so your GPS distance may vary. Always look ahead and run the shortest tangent if you safely can. Your GPS-tracked race, due to traffic not allowing you to run all tangents, or if you are not focused on running the shortest line, can over-measure the “official” distance. This is particularly the case on looped courses with many turns. Plan ahead for a faster than actual GPS pace on such race courses.
To get a good chest heart rate read, always wet the monitor straps before wearing. After acquiring heart rate to your device, jog a bit to let things settle down. Rinse chest straps using mild soap after use.
All heart-rate monitors can have variations and dropouts. In particular we have found this to be the case with chest straps that yield high readings in the first 10 or so minutes of a run. Low temperatures and humidity, hair, synthetic fabrics, etc., all can cause issues for heart rate monitors. Stopping for a few seconds can sometimes settle the rate down to more accurate levels.
It can be problematic to maintain accurate heart rate readings with wrist-based monitors while lifting weights, clenching bars, etc.
Shield wrist heart rate monitors from very bright sun, which can sneak under the band and interrupt the signal. Look for bands with a good light and cold air-free seal to your wrist. Wear wrist heart rate straps about an inch away from your wrist bone and tightly cinched.
When you first pair a heart rate or another sensor to a device, keep the two as close together as possible. The pairing wake-up signal can be weak.
If you have paired a sensor to a phone, keep the phone on the same side and plane of your body as the sensor. This will help avoid dropouts. This also applies to wrist heart-rate monitors and Bluetooth wireless headphones.