Yes, the surface definitely makes a difference. The sensor relies on timing the interval between foot strikes. If those strikes are not nice and distinct, things start to fall apart.

As a followup... I had another badly recorded run today. Logged 4.62 but was actually 4.0 so that's 15.5% off. Since I noticed the recorded pace was too fast during the run, I tried to concentrate on what could be wrong. As it happens, both wrong runs were earlyish in the morning and I was slogging through slippery snow. Normally the streets are dry enough because of the plows and cars but not during these two bad runs. So my foot would plant but slide a bit backwards as I tried to propel myself forwards and I'm wondering if that makes the sensor think my foot is in motion a lot quicker and longer.

Anyway, I agree the Sportband's granularity leaves a lot to be desired but it's still good enough most f the time.

Well... the 5k today was right. I guess I'll have to expect the Sportband to be messed up now and then. Thanks for the input.
--Joe

Even when you have more variance in your Sportband runs (bigger spikes) those spikes also snap to a set of fixed levels. Almost like the snap-to-grid feature in something like Photoshop. Getting distance measurements every 10 seconds from a pedometer/accelerometer is tricky and this artificial limiting of the readings is working against you. It's a bit like asking people to guesstimate the height of a tree. You might get guesses of 30ft, 33ft, 28ft and 27ft. Let's say the actual height of the tree is 29ft. These guesstimates when averaged (actually a least squares regression in our case) gives you 29.5ft.

But, now introduce this limiter that says you can only guess 25, 30 and 35. Those previous 4 guesstimates might now become 30, 35, 30 and 25. In this case we get 30.0ft instead of 29.5 so we are still getting close. But that 27ft guess that we snapped down to 25 could easily have snapped to 30 instead and if it did we would suddenly swing up to an average of 31.25.

The point of all this is that this artificial granularity limitation in the Sportband creates instability. You may get lucky 18 times in a row, but then on the 19th you get a series of 27's turned into 30's in a row and suddenly your overall distance is way out of whack. And I call this an artificial limitation because the sensor that is doing the actual measurement is the same between the Nano and the Sportband. The Sportband just receives the signals from the sensor and records them. I see no reason for it to not record them in the exact same way as the Nano.

Interesting... thanks for the insights. I've how some of my charts are artificial looking but others are spiky. Since I've run this neighborhood many times for the past year, it seemed to worked out to my normal distances/paces so I assumed that's the readings the Nike+ provided. I didn't realize the Sportsband read data differently than the pods.

The results have been great for 18 out of 19 runs so I hope it was a minor glitch or I'll have to look to other gear. I'll check in after my next run. Tomorrow and Tuesday look runable at about 30 degrees...... no comments from you 60 degree California folks, please :p

I have always been very suspicious of the Sportband. It has some serious granularity problems when
it comes to the 10-second sampling it does. If you look at
run#342912362
note how regular the grey line is. The peaks and valleys are all exactly at the same level.
That's extremely artificial. Compare that to the run below which is from an iPod Nano. The peaks and
valleys are quite random. I don't see how you can get accurate data out of a Spotband when this
device relies entirely on getting a little bit of signal out of a lot of noisy data. If you filter the noisy data
you obscure the signal.
run#1685266788

This has nothing to do with Slowgeek.com but I thought I'd ask if anyone has seen this problem. I calibrated a walk and a run when I got the Nike+/sportband five weeks ago and have done about 70 miles. I checked every few runs and they were within 1-3% according to google maps which is all I need.

But today I ran a real 4 miles (3.95) and Nike says it was 5 (5.04)! Nothing that I can control has changed... shoes, surface, neighborhood, sensor position/orientation/mounting. No injuries that would change the stride. That's 28% off!

I'll try to check in and report my next run tomorrow or Tuesday.