The following text is courtesy of Polar OY Finland - please do not reproduce without their permission. Thank you. Please note, it is basically the same technology used by Polar, Suunto, Garmin and Nike, currently all of these manufacturers use DynaStream to make their foot pods.

The following test was conducted in 2006. The FOOT POD's have moved on CONSIDERABLY since then. We use both GPS and FOOTPOD for races from 5K to full marathon. Are they any different, is one better than the other ? Not really. If you don't need to see your TRACK on a MAP, then get a discrete FOOT POD. If you want to see where you've been on a map, get a GPS.

The NEW Suunto Foot POD, 2011, is the same as the Garmin one. Both made in the same factory. Both will give 98% accuracy for 98% of runners, straight out of the box

The internal inertial sensors measure the acceleration of the foot pod more than 1000 times
per second and use this data with advanced algorithms to calculate foot angles and gait
velocity. These FOOT PODs are NOTHING LIKE PEDOMETERS. You do NOT enter your stride length, nothing like that. They are very advanced running speed sensors. On average, you can expect 97% accuracy out of the box, this can then be further calibrated to give even more accurate measurement.

This document was prepared in 2007 - however, the main details are still valid.

Q: Why didn't Polar use GPS technology for SD for the S625X / RS200 Running Computer?
We (Polar OY) considered both GPS and inertial technologies carefully before choosing to go with
inertial technologies. GPS has some positive elements but we chose the best overall
technology for running anywhere and in any conditions.
We recognized that existing GPS was too heavy and consumed too much power for an
application that was meant for runners who are demanding and relatively heavy users
and train frequently. Existing GPS applications are simply not as practical for someone
who is running frequently because of the need to constantly recharge/replace batteries
and because of the discomfort of hauling abound a large GPS unit on the upper body.
When used in a real life running scenario- GPS is no more accurate that inertial sensor
technology. With inertial technology we saw that we could provide the best solution for
runners who want accurate and reliable speed and distance measurement that performs
in all conditions (indoors and outside), in urban city settings with tall buildings, even in
very heavily wooded trails and twisting turning trails and tight turning paths.

Q: GPS technology is considered advanced by many. What about the Polar inertial
sensor technology that Polar uses?
The inertial technology that Polar uses is very advanced, inertial technology is used in
aerospace positioning and guidance systems, industrial robotics and in advanced
automotive applications such as active suspensions and emergency airbag deployment
to name a few.

Q: GPS provides speed and distance while running, cycling and even during X-C
skiing. What about the Polar S625X?
The Polar S625X was designed primarily for runners and tri-athletes. So we have
ensured that the running functions are optimized for running and cycling. The S625X is
fully compatible with all Polar cycling sensors. Combining cycling speed and cadence
and power options provides many more dimensions to the cycling cross-sports
experience than that offered by GPS speed and distance unit.

Q: Some GPS units provide directional features to help navigation. Why has Polar
opted to leave this out in the S625X / RS200SD?
The S625X / RS200SD were designed with the knowledge that 80% of runners generally run the
same 3-5 routes. The speed and distance element of the S625X / RS200SD will support people who
want to track speed and distance on these routes and also lets them find more new
routes with no need for external mile markers. Navigation features are
best suited for outdoor and adventure products, while the S625X / RS200SD is focused on providing
runners the most relevant features for building performance and enhancing their every
running experience.

Q: Is the S1 footpod heavy?
You can't feel it when once its attached to your shoe. Infact, you will struggle to figure
out (by feel) which shoe has the footpod on it once you put it on. The Polar S1 footpod is
built to last with robust water resistance, shock resistance and easy battery change while
still not reducing shoe comfort or running performance.

Q: How accurate is the S625X / RS200SD ?
Generally the S625X / RS200SD is at minimum 97% accurate even without calibration. The
accuracy increases to 99% with calibration. In relative terms, this accuracy is as good or
better than the accuracy provided by GPS. Interestingly, this degree of accuracy is
generally far better than what is seen on running treadmills. Have you ever heard of a
runner complain that a treadmill was not accurate enough for their training purposes?

Q: Do I need to re-calibrate my footpod everytime my foot pod or wrist unit battery
is changed?
If you choose to calibrate your Polar S1 foot pod, the calibration factor will be stored in
the permanent memory of the S625X / RS200SD Running Computer. This calibration will be stored
permanently, unless you decide to change it....so if you calibrate, you only need to do it
once.

Q: Will the Polar S1 foot pod leak water?
Robust water-resistance and durability are key elements in the design of the Polar S1
foot-pod. It will survive immersion, wet running environments and continue to perform
reliably. However, the S1 was not designed for swimming or aqua-running so please do
not going swimming with it.

Q: What is the foot pod battery lifetime?
The battery lifetime is 20 hours of use in average.

Q: How do I know that the foot pod battery needs to be replaced?
When the green light on the foot pod turns red, you need to replace the battery.
Replace the battery in case the foot pod does not start or the running speed shows 00
constantly.

Q: Can I replace the battery myself if so, what is the battery type?
The foot pod is designed so that the user can replace the battery him/herself without
tools.The battery type is AAA.

THE FOLLOWING TEXT WAS TAKEN FROM www.suunto.com

The Suunto Foot POD is a lightweight wireless enhancement for your Suunto t3, Suunto t4, or Suunto t6 that enables you to measure and record speed and distance information in real-time. Speed limit alerts warn you if you stray above or below your personal limits, making the Suunto Foot POD the ideal tool for marathon pacing and mixed-intensity training. For interval training, the ability to capture running speed and distance, as well as automatic lap times and distances, makes the Suunto Foot POD an invaluable training companion.

An easy-to-use clip firmly attaches the Suunto Foot POD to your shoelaces, keeping it in place when you're running in even the most demanding conditions. With up to 200 hours of use from one battery - three times longer than before - you'll be able to keep track of all your vital training data.

The Suunto Foot POD complements your Suunto heart rate monitor and Suunto Training Manager software. The combination of your run data and physiological data provides a complete picture of your training. After your run, you can use Suunto Training Manager software to view speed profiles and graphs for comprehensive post-training analysis.

• Lightweight (27 g/0.95 oz including battery)
• Wireless transmission (up to 10 m/30 ft)
• Water resistant to 30 m/100 ft
• Disturbance-free ANT transmission technology
• Operating temperature: -20°C to +60°C/5°F to 140°F
• For outdoor AND indoor use
• Speed measuring range: 1.5 - 5.5 m/s = 4.5 - 16.5 ft/s = 5.5 - 20 km/h = 3.4 - 12.4 mph
• Speed limit alarms
• Average speed
• Lap distance and automatic lap times
• User-replaceable battery