Can I comment on a few posts. It’s a little off topic but will answer a few questions about which one
First the price dumps are in anticipation of the release of the new 410 model. The 410, 210 and 110 are improvements on the predecessor models using lessons learned from the 405 set up.
The 205 and 305 are the same with regard to form and function. The difference is in the ability to pair other fitness devices with the receiver; including the HR monitor, foot pod, cadence transmitter (bike). So if you think you may want to pair a device then go with the 305. If you are looking for a device that will let you know how far and how fast, then the 205 is you solution.
The 405 as described is more like a watch and the numbers are much smaller. I have 2020 vision with contacts and have issues with the device. The advantage of the 405 is a much satellite receiver that works better in heavily treed or downtown situations. The bezel operation is not all that swift if you are nearing the end of a long run and want to flip through data. The 405 talks with your computer easier than the 305/205 model through the use of the ANT+ technology.
The foot pod - All foot pods must be calibrated. The really nice thing about the Garmin foot pod when paired with a Forerunner is that you can calibrate through GPS. Just with the receiver in calibrate and run about a kilometer and it will let you know when it is calibrated. The more accurate way of calibration is to take it to the track and run between 800 and 1600 meters (2-4 laps) in the inside lane. When calibrating make sure to run like you plan to in training and in the race. i.e. run walk if you plan to run walk. The device works through an accelerometer so walking and running will produce differing force patterns to the device. Also, as you train for a long event I would make sure to recalibrate every 4-6 weeks. As you grow stronger through the training season your stride will change… maybe enoungh to force a calibration. Once you are calibrated, do not be surprised if your favorite treadmill indicates a speed 10% higher than it actually runs. Many TM manufactures set speed at the factory a little high to make customers feel better about performance while on their equipment.
The 310XT is a waterproof upgrade of the 305 but incorporates the 405 antenna technology. If you are a triathlete, this may be the unit for you. Personally, I do not think I would wear this in a triathlon as I would be afraid of losing the unit. I have lost a watch in a race – must remember tape in the race bag to tape up the buckle.
Finally, for the bare minimum, there are several interval timers combined with stop watches that will help hold your interval times and give you time run. The Ironman and Soleus lines are the better known examples. When I first started on this journey I had a 100 lap Timex IM watch and would hop in the car and drive my routes. Things have changed a lot and for the better.
Hope this helps some.