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        General >> Off Topic Subjects >> which is more accurate ?
        
(Message started by: craig on Sep 19^th, 2006, 5:09am)

Title: which is more accurate ?
Post by craig on Sep 19^th, 2006, 5:09am

quickie.... ;D

which is more accurate,the speedo in the car,or the speedo on my sat nav ???,can be upto a 15 MPH difference at times... :o

Title: Re: which is more accurate ?
Post by Daven on Sep 19^th, 2006, 7:11am

I would say the speedo is more consistent - the satnav can be affected by trees and bad reception (as we found out last week down your way :) ). But baring in mind the speedo shows a faster speed than you are actually doing the satnav can give you a more acurate avarage speed IMO

;)

Title: Re: which is more accurate ?
Post by Kjetil S on Sep 19^th, 2006, 7:20am

With good reception, the sat. nav. has the better chance of showing a correct reading as they calculate the distance you have moved (give or take some meters) in the last second and should use the satellites as clock source. (Atleast if the programmer was sane ;D)

Title: Re: which is more accurate ?
Post by Daven on Sep 19^th, 2006, 7:33am

on 09/19/06 at 07:20:49, Kjetil S wrote:

In a straight line it would be accurate, thats why I think it has to be avarage speed ;)

Dave

Title: Re: which is more accurate ?
Post by Bren on Sep 19^th, 2006, 10:23am

When using a sat nav with a calibrated tachograph, which must be ±2%, the speed reading on the sat nav is broadly the same.

Title: Re: which is more accurate ?
Post by Dave on Sep 23^rd, 2006, 8:17pm

Doesn't it depend on hills? GPS I think measures speed across the planet. So you could be doing 70mph up a hill yet you may only be doing 60mph as far as the sat nav is concerned.

Or am I talking rubbish ;D

Title: Re: which is more accurate ?
Post by Kjetil S on Sep 23^rd, 2006, 8:34pm

With enough satellites to triangulate, it _should_ be possible to work out movement in all three dimensions (that means even uphill ;D)

But yes, gps units do tend to be more inaccurate when it comes to height, although I don't think it will effect the reading too much. Atleast not to the point where it says 60 and you're doing 70.

Title: Re: which is more accurate ?
Post by Dave on Sep 25^th, 2006, 12:05pm

Half right. Close enough for me ;) ;D