iSport - power fluctuations

[aldolibersan]

I've just had my iSport for about 2 weeks now and have redone the cal rides a number of times, just to make sure I am getting it right.
I made sure I did the following:

1. set the altimeter
2. let the iSport acclimatize to the temperature for 15 minutes
3. set the wind offset
4. checked the tilt
5. did the cal ride with literally no wind (less than 5km anyway)

What i am finding is that the power fluctuates quite a bit, probably 20-30 watts most of the time. Which is not so bad in that I can usually notice where the middle point is which ends up being the average anyway. But, I've noticed that as soon as I start up a hill the power reading increases to much higher than what it should be (at least by perceived effort anyway) and then gradually settles down. However, I live in a farily rolling to hilly area and many of the hills are short and steep 200-300 meters/7-12%. I am wondering what I can do to try and smooth this out? Also, any suggestions on best practices for coast downs? My functional power threshold is about 260watts. So, I am wondering if I should be doing the coast downs? I have tried a couple of them already but find that after I've done them them power fluctuates even more wildly and the power readings are much higher than they should be (good for the ego, but not reality). I think I must be performing the coast down wrong.

[coachboyd]

Sounds to me like everything is working perfectly.

Power numbers will fluctuate as you ride. You have to realize that every second you are getting a reading of how many watts your legs are pushing. When you get to a short steep hill, your watts will go pretty high for a short period before settling in. Likewise when you finish the hill and start down the other side, power numbers will drop off dramatically. On a course with rolling terrain you will have a much higher variability in wattage. . .this is common.

What you can do to check your calibration is to go into the setup screen. Scroll to the *coast* screen and leave that up as you coast down a hill in your normal riding position. If the number being shown is within +-20 watts at about 25 mph, then you are good to go. If it's more or less, then I would recommend doing another coastdown.

For the best coastdown, make sure you do a tilt and wind offset. Then find a road in good condition, sheltered from the wind. A bowl shaped road is great for doing coastdowns, you can use the downhill to get up to speed and the flat and uphill to slow you down. I have found a good coastdown usually lasts between 20-30 seconds.