Garmin type things

colly

Re member eR
Location
Leeds
They are not exactly accurate are they?
I took two with me when l went out today.

One recorded 3.8 miles.....the other 4.2 miles.

One recorded max speed at 23.5 mph
The other 25 point something.
One showed 264 ft of climbing the other 215ft.
Different max gradients, heart rates etc as well.

I know satellites move about etc and results are a 'good average' but I'm surprised the devices weren't either showing exactly the same or at least within a spit of each other.
 

ColinJ

Puzzle game developer
They are not exactly accurate are they?
I took two with me when l went out today.

One recorded 3.8 miles.....the other 4.2 miles.

One recorded max speed at 23.5 mph
The other 25 point something.
One showed 264 ft of climbing the other 215ft.
Different max gradients, heart rates etc as well.

I know satellites move about etc and results are a 'good average' but I'm surprised the devices weren't either showing exactly the same or at least within a spit of each other.
Did you make sure that you had a good satellite lock on both of them before setting off?

Some devices are much quicker than others to lock on.

My 14 year old Etrex can take 1-2 minutes, but my 3 year old phone can get a lock in less than 10 seconds. GPS chips have improved a lot over the years!

If I start moving before the lock has been achieved, the Etrex can get very confused. I once had it tell me that I was in Halifax when I was actually still 8 miles away in Hebden Bridge. That was before I discovered the satellite lock thing.
 

Edwardoka

Prolix Maximus
How did you measure separate heart rates (or did you pair them both to the same HR strap?)

Regarding GPS data, max values will often highlight the least accurate data point and can usually be ignored. Averages are generally much more accurate, though 0.4 miles is a lot of drift over 4 miles, have you uploaded the rides anywhere?

The main methods for measuring altitude will give wildly different results. In an extreme example I've seen a ride of about 10,000 feet climbing be recorded as 18,000 feet when in reality the GPS accuracy meant that the recorded position kept dropping off a roadside cliff and snapping back.
 

I like Skol

Hold my beer and watch this....
For a long time I have argued the point that old fashioned wired or wireless cycle computers are far more accurate (providing the wheel size is set correctly and calibrated on a decent ride of known distance)
Many supporters of gps tech have disagreed for various reasons, despite the fact there is not a lot that can be more simple than a sensor physically counting the turns of the wheel?
Now it appears you can buy an add-on sensor for your gps to improve accuracy :wacko:

My experience shows the gps systems usually slightly under records the distance. I suspect this is due to minor signal losses and from the ride trace cutting corners etc.
 
OP
colly

colly

Re member eR
Location
Leeds
Solved the problem.
I looked at the metrics just now and lo and behold the Garmin indicating the longer ride was switched on a couple of hours before the other one, which was turned on just before the ride. I must have pressed the 'start' button when I plugged it in to get a bit of charge in it.
So while it was just sitting on the table for 2 hours I am guessing that the various satellite movements will have it sort of jigging about a bit. Hence recording distance.
I'm off down to my sons place later and I'll see what the results are later.
 

fossyant

Ride It Like You Stole It!
Location
South Manchester
My two have been fairly accurate.
 
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