So within a week of getting my new Garmin Forerunner 910XT I have updated the firmware from version 2.20 to version 2.40 as per a tip from DC Rainmaker.
I have noticed wild fluctuations in the pace the unit is displaying whilst I am running: flashing between 3:37min/km (impossible, believe you me), to over 7.30min/km (possibly, but surely not at the time). I had hoped that this update would fix this problem, but it is still happening.
It appears to be just the display of your actual pace whilst in Run mode. I am not experiencing similar problems in Bike mode, and the calculations once the data is uploaded to GarminConnect seem in order (I assume there is a whole lot of data smoothing happening). I certainly have never experienced anything like this on my Garmin Forerunner 305.
The open-water GPS capabilities are also suspect. The map below (embedded from GarminConnect) is of a swim I did up at Silvermine Reservoir. I was swimming straight lengths using the metal structure in the centre of the wall and the short wooden bridge at the top as my sighting points. As you can see, I ended my workout by swimming straight through the Silvermine Reservoir wall, down the 15-odd meter drop and through the fynbos below: just call me “Dambuster Dave”! And I can assure you while I may not be able to swim in a perfectly straight line, I was sighting off some fairly obvious landmarks, and did not swim nearly that off-course!
I have spent some time online and found a number of people mentioning similar problems with the run pace. What I assume is an official Garmin forum Administrators has acknowledged the problem, and mentioned a firmware update to fix this. Many forum members have offered the helpful advice that I should use the average pace over kilometre splits instead; let’s be clear: this is not an acceptable solution to something that is clearly a problem with a high-end unit, especially considering the problem did not exist in it’s (lower-end) predecessor.
Let’s hope there is another update real soon!