Discrepancy between odometer and sat nav
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Discrepancy between odometer and sat nav
Hi,
Just got back from 3 weeks in Spain and having driven quite some distance we've noticed that the odometer is claiming we've travelled further than the sat nav.
It's work out at about an extra mile for every 40.
Should I get this looked at/have the odometer recalibrated or ignore it?!
Cheers...
Just got back from 3 weeks in Spain and having driven quite some distance we've noticed that the odometer is claiming we've travelled further than the sat nav.
It's work out at about an extra mile for every 40.
Should I get this looked at/have the odometer recalibrated or ignore it?!
Cheers...
Re: Discrepancy between odometer and sat nav
The satnav assumes you've been travelling on a flat road with no hills so it is likely to always be behind the odometer.clummzie wrote:Hi,
Just got back from 3 weeks in Spain and having driven quite some distance we've noticed that the odometer is claiming we've travelled further than the sat nav.
It's work out at about an extra mile for every 40.
Should I get this looked at/have the odometer recalibrated or ignore it?!
Cheers...
If the satnav is looking vertically down at you travelling up a 1 in 1 hill (unlikely I know but it helps the arithmetic) it sees you travel half a mile, but looking sideways at the road you will see that it is actually a mile long and that is the distance the odometer measures.
Re: Discrepancy between odometer and sat nav
I think thats fairly accurate actually.
Our old Freda's speedo (so presumably the odometer) was about 5/6% fast according to the GPS.
Remember too that the GPS reading is a flat linear reading, ie it does not take into account the extra mileage up and down hills, could account for quite a bit if you were in the hilly bits.
Our old Freda's speedo (so presumably the odometer) was about 5/6% fast according to the GPS.
Remember too that the GPS reading is a flat linear reading, ie it does not take into account the extra mileage up and down hills, could account for quite a bit if you were in the hilly bits.
Re: Discrepancy between odometer and sat nav
Of course, that makes perfect sense!
Thanks for the replies
Thanks for the replies
- widdowson2008
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Re: Discrepancy between odometer and sat nav
Apologise for this scanner but 'numbers' are my thing.scanner wrote:
The satnav assumes you've been travelling on a flat road with no hills so it is likely to always be behind the odometer.
If the satnav is looking vertically down at you travelling up a 1 in 1 hill (unlikely I know but it helps the arithmetic) it sees you travel half a mile, but looking sideways at the road you will see that it is actually a mile long and that is the distance the odometer measures.
Theory is spot on scanner but the maths aint - sorry.
The theoretical 1:1 hill (1 horizontal and 1 vertical) gives a gradient length of 1.414....
.....and so, to use your phrasing, looking straight down, the satelite sees 1 mile, but looking sideways the hill is actually 1.414... miles long, and as you say, the odometer will read 1.414..
Coat on - I'm off........
Steve
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Re: Discrepancy between odometer and sat nav
Scanner, why didn't you tell us this before?!
There's been talk on here about checking speedos against sat navs, and odometers likewise, and although I'm reasonably happy that mine's not too far out, from what you are telling us there is little point in checking my odomoter against the sat nav round here! I doubt there's a level mile within 10 miles of here Cambridgeshire, on the other hand, would be a much better place to try it
Seriously, good explanation, and thank you
There's been talk on here about checking speedos against sat navs, and odometers likewise, and although I'm reasonably happy that mine's not too far out, from what you are telling us there is little point in checking my odomoter against the sat nav round here! I doubt there's a level mile within 10 miles of here Cambridgeshire, on the other hand, would be a much better place to try it
Seriously, good explanation, and thank you
Alison
The traveller sees what he sees, the tourist sees what he has come to see. (G K Chesterton)
The traveller sees what he sees, the tourist sees what he has come to see. (G K Chesterton)
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Re: Discrepancy between odometer and sat nav
That explains why my satnav and speedo discrepancy varies - never thought of hills
John
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(Evidence that intelligent life exists in the universe, is that it hasn't tried to contact us)
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Re: Discrepancy between odometer and sat nav
Do you know what they are?francophile1947 wrote:That explains why my satnav and speedo discrepancy varies - never thought of hills
Alison
The traveller sees what he sees, the tourist sees what he has come to see. (G K Chesterton)
The traveller sees what he sees, the tourist sees what he has come to see. (G K Chesterton)
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Re: Discrepancy between odometer and sat nav
Of course I live on one Norfolk is only really flat when you get to the fenland areas, which are shared with Cambridgeshire and Lincolnshire, although the Broads aren't very hillyAlison01326 wrote:Do you know what they are?francophile1947 wrote:That explains why my satnav and speedo discrepancy varies - never thought of hills
John
(Evidence that intelligent life exists in the universe, is that it hasn't tried to contact us)
(Evidence that intelligent life exists in the universe, is that it hasn't tried to contact us)
Re: Discrepancy between odometer and sat nav
widdowson2008 wrote:Apologise for this scanner but 'numbers' are my thing.scanner wrote:
The satnav assumes you've been travelling on a flat road with no hills so it is likely to always be behind the odometer.
If the satnav is looking vertically down at you travelling up a 1 in 1 hill (unlikely I know but it helps the arithmetic) it sees you travel half a mile, but looking sideways at the road you will see that it is actually a mile long and that is the distance the odometer measures.
Theory is spot on scanner but the maths aint - sorry.
The theoretical 1:1 hill (1 horizontal and 1 vertical) gives a gradient length of 1.414....
.....and so, to use your phrasing, looking straight down, the satelite sees 1 mile, but looking sideways the hill is actually 1.414... miles long, and as you say, the odometer will read 1.414..
Coat on - I'm off........
I've just propped a 1ft/30cm ruler at a 45degree angle (1 in 1) on top of my calibrated paper trimmer and yes it measures nearer 8"/20cm than 6"/15cm from lower end to vertical line down from upper end.
BUT it certainly doesn't measure 1ft/30cm - how could it?
By your reckoning if I stand it at 90degrees it should still appear to be 1ft/30cm long when viewed from above and it doesn't - it vanishes.
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Re: Discrepancy between odometer and sat nav
Not too good at words - I'll post a diagram in 2 minsscanner wrote:widdowson2008 wrote:Apologise for this scanner but 'numbers' are my thing.scanner wrote:
The satnav assumes you've been travelling on a flat road with no hills so it is likely to always be behind the odometer.
If the satnav is looking vertically down at you travelling up a 1 in 1 hill (unlikely I know but it helps the arithmetic) it sees you travel half a mile, but looking sideways at the road you will see that it is actually a mile long and that is the distance the odometer measures.
Theory is spot on scanner but the maths aint - sorry.
The theoretical 1:1 hill (1 horizontal and 1 vertical) gives a gradient length of 1.414....
.....and so, to use your phrasing, looking straight down, the satelite sees 1 mile, but looking sideways the hill is actually 1.414... miles long, and as you say, the odometer will read 1.414..
Coat on - I'm off........
I've just propped a 1ft/30cm ruler at a 45degree angle (1 in 1) on top of my calibrated paper trimmer and yes it measures nearer 8"/20cm than 6"/15cm from lower end to vertical line down from upper end.
BUT it certainly doesn't measure 1ft/30cm - how could it?
By your reckoning if I stand it at 90degrees it should still appear to be 1ft/30cm long when viewed from above and it doesn't - it vanishes.
Steve
Re: Discrepancy between odometer and sat nav
scanner wrote:widdowson2008 wrote:Apologise for this scanner but 'numbers' are my thing.scanner wrote:
The satnav assumes you've been travelling on a flat road with no hills so it is likely to always be behind the odometer.
If the satnav is looking vertically down at you travelling up a 1 in 1 hill (unlikely I know but it helps the arithmetic) it sees you travel half a mile, but looking sideways at the road you will see that it is actually a mile long and that is the distance the odometer measures.
Theory is spot on scanner but the maths aint - sorry.
The theoretical 1:1 hill (1 horizontal and 1 vertical) gives a gradient length of 1.414....
.....and so, to use your phrasing, looking straight down, the satelite sees 1 mile, but looking sideways the hill is actually 1.414... miles long, and as you say, the odometer will read 1.414..
Coat on - I'm off........
I've just propped a 1ft/30cm ruler at a 45degree angle (1 in 1) on top of my calibrated paper trimmer and yes it measures nearer 8"/20cm than 6"/15cm from lower end to vertical line down from upper end.
BUT it certainly doesn't measure 1ft/30cm - how could it?
By your reckoning if I stand it at 90degrees it should still appear to be 1ft/30cm long when viewed from above and it doesn't - it vanishes.
Are you disagreeing with Pythagoras Scanner ?
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Re: Discrepancy between odometer and sat nav
Just ask Pythagorus
I don't think scanner was trying to be spot on, just demonstrating the principal involved
I don't think scanner was trying to be spot on, just demonstrating the principal involved
John
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Re: Discrepancy between odometer and sat nav
Here we go.
To my understanding, hill gradients are quoted in the format 1:100 which translated into English means for every 100 feet travelled forward (horizontal), you will actually climb 1 foot.
In your previous example of a bloody steep hill 1:1, this means that for every 1 foot you travel forward, you will climb 1 foot, as shown in the diagram, but the actual distance you travel will be 1.414...
ie: satelite sees 1 foot whilst distance travelled is 1.414
Hope this explains what I was getting at.
To my understanding, hill gradients are quoted in the format 1:100 which translated into English means for every 100 feet travelled forward (horizontal), you will actually climb 1 foot.
In your previous example of a bloody steep hill 1:1, this means that for every 1 foot you travel forward, you will climb 1 foot, as shown in the diagram, but the actual distance you travel will be 1.414...
ie: satelite sees 1 foot whilst distance travelled is 1.414
Hope this explains what I was getting at.
Steve
Re: Discrepancy between odometer and sat nav
Well there is where you are going wrong ..........
I said a mile TRAVELLED uphill, so now redo your diagram with the slope of the "hill" as the 1 not the horizontal and vertical distances.
Perhaps I should have said "it sees you travel 0.8(ish) of a mile whereas the side view and the odometer shows you have actually travelled 1 mile".
Where did you get the idea I had driven 1.414miles up the hill? I didn't say that.
I'm not disagreeing with Pythagorus
I said a mile TRAVELLED uphill, so now redo your diagram with the slope of the "hill" as the 1 not the horizontal and vertical distances.
Perhaps I should have said "it sees you travel 0.8(ish) of a mile whereas the side view and the odometer shows you have actually travelled 1 mile".
Where did you get the idea I had driven 1.414miles up the hill? I didn't say that.
I'm not disagreeing with Pythagorus