Random (but not really)

Friday, March 21, 2014

Pedometer Testing: THIS IS NOT HOW MATH WORKS

I’ve thought from the start that the Withings had a wonky way of measuring elevation, but I pretty much ignored it.

But today I decided to take the GPS on our walk into town, and compare the GPS elevation rise to what the pedometers were giving me.

Now, from everything I’ve read, the FitBit gives you ten feet of elevation for every floor climbed. That’s easy enough.

But the more I looked at the Withings data, the less sense it made. So this evening I decided to sit down and try and figure out just what the hell the Withings data was trying to tell me.

For my walk, I wrote down the starting elevation and the ending elevation.

My numbers were 1619 ft and 2026 ft, which gave me a change in elevation of 407 ft.

Then I asked Michael to see if he could give me his elevation gain from the website.

His number was 95 ft.

Wha?

So, I go to the website, and get the elevation gain for each 30 minute time period.

Withings-elevation-fri-5

Can you read that number? The time is from 6:30 to 7:00 and it gave me 92 ft and 30 floors. Adding the numbers for the three 30 minute periods (16/6, 0/0, 92/30) I get an elevation gain over 90 minutes of 110 ft.

100 != 407

So, I note flights and elevation for every 30 minute time period [(14, 2, 13, 2, 6, 7, 1, 8, 35, 24, 4, 20, 9, 3, 3, 2, 6, 30, 5, 1, 8, 4, 1 flights) and (44, 7, 40, 8, 19, 22, 4, 25, 105, 74, 14, 60, 28, 9, 10, 7, 18, 92, 17, 3, 25, 12, 3 feet)] and I get a total of 646 feet and 208 flights of stairs.

Look back at the image. It’s giving my total elevation gain for the day: 2190 ft. None of those numbers seem to have any relationship to each other.

I fully admit that simple math is not my strong point, but I don’t see how my daily elevation gain total can be three and a half times higher than the sum of the individual time periods.

I’ll also note that the 646 ft measurement is much closer to what the FitBits gave me, (assuming 10 ft elevation rise per flight of stairs) an elevation gain of 640 or 670 feet (64 and 67 flights of stairs) for the day.

This… this makes no sense. And even assuming the sum of the individual time periods give me the correct elevation gain, the flights of stairs it gives are ridiculous, unless the Pulse things that a flight of stairs is only three feet high.

So, now I truly, deeply doubt the information the Pulse has been giving me–at least anything beyond basic step count.

Powered by WordPress

This is text at the bottom of the page.

Discover more from Random (but not really)

Subscribe now to keep reading and get access to the full archive.

Continue reading