How accurate is the step counter in the health app on the iPhone

I Just did several tests for accuracy. First I took 100 steps with the phone in my cargo pocket and it counted 129. Then I took 100 steps with the phone in my side pocket and it said 108. Then I took 100 steps with the phone in my jacket pocket and it said 98.

Then I took the advice to enter my height and weight into the health data. And I did the same three tests. Now the results were: Cargo pocket: 139 steps. Side pocket: 107 steps. Jacket pocket: 102 steps.

Looks like the jacket pocket wins hands down. For the record it's a side pocket on my jacket.

Its been more then a year I am using Health apps actively for Steps counts, Heart rate, and other health info on my iPhone 5S.

I frequently go for trekking, with my friends having iPhone 6S.

Every time I found there is huge difference in steps counts in different phones.

Being an iOS Developer I started digging inside to understand how it works.

Basically it uses iPhone motion sensor Class name "CMPedometer"

so whenever device get motion steps counts get started. it doesn't matter with GPS.

so even your not running/walking, just sitting on chair but you moving your device in 10-20 inch area, boom!! there you will get after few seconds steps counted get updating.

I have sent my feedback to apple developer guys regarding this. even there was trekking day i walked around 52-55 km. but application showed only 28Km and steps counts were 7453.

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"so its the motion not time or GPS which matters here"

I don't find it accurate at all! Today, I walked 3 miles but on my iPhone pedometer is 1.8! That's not even close. I measured the distance using google maps and also using my car.

I know that mine is way less than measured, apple please fix this, it was the main reason I bought it!