I like this thing quite a lot. I've had it for about three weeks, and have used it on 12 workouts so far. I use it primarily for running, with biking a secondary usage. The main reason I wanted it was for the instantaneous readout of distance, running pace and heart rate, the latter needed for the speed work I want to do this running season.
The core functionality (distance and heart rate monitoring) works perfectly. There's none of the signal drops I've had with other heart monitors. Once the satellites are initially acquired, I've only had one dropout when I was outside. The initial acquisition of the satellites can be quirky and can take some time. The accuracy (according to the readout) is +/- 25ft, depending on how many satellites can be found. I've compared the distance measurement on the GPS with a known, measured distance on one of the trails I run on (the Chicago lakefront path). The GPS always increments a mile when I'm within 5 or 10 feet of the mile marker sign on the path. Well, I guess that's the least I should expect from a $350 GPS unit! Of course it's bigger than a normal running stopwatch, but that hasn't bothered me at all. The heart rate strap is also very comfortable and well-designed.
The display is crisp and has one outstanding feature: The information presented on the various pages can be completely user-customized. The default screen layout is rather poor, but in just a few steps I could replace it with the information I wanted to see while I run. There are almost 40 different data fields you can choose from for display. Examples: current pace, average lap pace, average run pace, heartrate, distance.
The only disappointment is the point-in-time (instantaneous) pace measurement: It varies wildly during a run. I see swings as big as +/- 3 minutes/mile. I'm a marathoner and I know my pace is fairly consistent during a run. I just looked at my run today, and according to the data the first mile varied from 5:57/mile to 12:06 mile. I suspect the problem is either in the averaging algorithm (too short a distance?), or in the uncertainty that results from different satellites coming in and out of view. The variations seem to get worse under tree cover compared with an open area. Luckily there's a lap-average pace that can be presented, and at least that value is useful and more accurate. The bottom line is that you can't look at the watch and say "right now I'm running 9 mins/mile". There is the ability to specify a pace smoothing factor, but I have it maxed out and still see the variations. The elevation readout also seems inaccurate, but that isn't important to me.
Upload of workout data to the PC software (Training Center) is transparent. The PC software is very good for presenting time/distance/pace/heartrate/calorie data. However the maps it shows are very crude. I've worked a bit with one of the online, subscription services (MotionBased). That looks really good and provides some additional functionality beyond the included Training Center software, although I still haven't decided if it's worth the $$$ yet for long-term data storage. MotionBased allows export to Google Earth, and it's tremendously cool to see your running path superimposed on a satellite image. You can recharge the unit through the USB port on your computer, although it's slower than using the dedicated recharger.
I had hoped that owning this device would prove motivational for me, and indeed it has. I can't imagine running or biking without it. Updating my training log is trivial now: Plug this thing into my computer, and it's done. My hope is that a future software update will do something about the pace calculation (maybe a few additional levels of smoothing?). If so, the Forerunner 305 would earn 5 stars+++.
Positives:
Flawless heart rate sampling
Great distance measuring and lap-average pace calculation
Seamless integration with a PC
Fully-automatic training log update
User-customizable display
Negatives;
Wildly-varying pace readout.
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