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c2rm
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Joined: Aug 11, 2005
Posts: 20
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 Posted: Thu Sep 01, 2005 12:14 am Post subject: How accurate is the indicated speed? |
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Quick question for all you experts out there - running TT5 on an IPAQ4150 and have the acreen set to show me my speed. But, how accurate is it? If TT5 is indicating 70MPH will the motorway police pull me over or if it is showing 40MPH will the GATOS flash? etc etc etc
Any advice/opinion or fact grateful received :D
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Skippy
Pocket GPS Verifier
Joined: 24/06/2003 00:22:12
Posts: 2946
Location: Escaped to the Antipodies! 36.83°S 174.75°E
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| Posted: Thu Sep 01, 2005 12:18 am Post subject: |
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If you are travelling at a constant speed for several seconds on a flat road and in a straight line, with a good satelite fix then the GPS will typically give a speed reading which is accurate to 0.1 MPH
If your speed is changing then the speed indicated by the GPS will lag behind reality.
If you are going around a corner or up/down hill then the GPS will read slightly slow.
A car speedo will typically read 0-10% fast to allow for manufacturing tolerances, tyre wear, different brands/types of tyre etc.
The Police have special speedos calibrated in 1 mph increments and accurate to 1 mph so don't try and suggest to them that their speedo was reading fast. 
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tomo1340
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Joined: Jul 17, 2005
Posts: 209
Location: Bentham
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| Posted: Thu Sep 01, 2005 12:19 am Post subject: |
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Not a resident expert and I can't give you a solid answer other than it is believed your speedo is set to indicate you are going faster than you actually are. There is a big mobile screen thing near my house and it tells you your speed as you come down the road. My speedo read 32mph, while the gps and the screen read 28 so I am slightly inclined to agree.
Read this for more info http://www.pocketgpsworld.com/modules.php?name=Forums&file=viewtopic&t=27003 |
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c2rm
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| Posted: Thu Sep 01, 2005 12:24 am Post subject: |
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| Thanks for the advice. It is as I suspected but I just wanted to be sure that there wasn't some deliberate error programmed into TT to try and keep people's speed down. :D :D |
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Masked-Marauder
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Joined: Aug 18, 2005
Posts: 89
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| Posted: Thu Sep 01, 2005 12:25 am Post subject: |
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| I use a calibrated speedometer at work and TTN5 is accurate, at least with my BT GPS unit anyway. |
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tomo1340
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Joined: Jul 17, 2005
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Location: Bentham
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| Posted: Thu Sep 01, 2005 12:35 am Post subject: |
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From what I gather from the thread I linked to it seems that a speedo can legally read higher than the actual speed you are going, but it can in no uncertain terms read under causing you to inadvertantly break the law.
I have been told that the police/speed cameras give you 10% leeway due to speedo inaccuracies, however a guy from my old work got stung in Preston twice in a few weeks doing 31mph and 32mph in a 30 zone so don't take that as gospal. |
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Masked-Marauder
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Joined: Aug 18, 2005
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| Posted: Thu Sep 01, 2005 1:44 am Post subject: |
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| tomo1340 wrote: |
I have been told that the police/speed cameras give you 10% leeway due to speedo inaccuracies, however a guy from my old work got stung in Preston twice in a few weeks doing 31mph and 32mph in a 30 zone so don't take that as gospal. |
The Ass of Chief Police Officers (ACPO) guidelines are 10% + 2mph as the prosecution threshold, so in a 30mph zone, 34 mph no prosecution, 35mph and your ticketed.
BUT they are only a guide, and the vocal minority are currently screaming that speeding is speeding an no lee-way should be allowed. Some forces, faced with falling revenue streams, are now adopting this approach. |
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Masked-Marauder
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Joined: Aug 18, 2005
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| Posted: Thu Sep 01, 2005 1:48 am Post subject: |
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| Masked-Marauder wrote: | | tomo1340 wrote: |
I have been told that the police/speed cameras give you 10% leeway due to speedo inaccuracies, however a guy from my old work got stung in Preston twice in a few weeks doing 31mph and 32mph in a 30 zone so don't take that as gospal. |
The  (Association) of Chief Police Officers (ACPO) guidelines are 10% + 2mph as the prosecution threshold, so in a 30mph zone, 34 mph no prosecution, 35mph and your ticketed.
BUT they are only a guide, and the vocal minority are currently screaming that speeding is speeding an no lee-way should be allowed. Some forces, faced with falling revenue streams, are now adopting this approach. |
Wow, how anal, censored for saying ass! That Megan ad was on TV this afternoon, how did it go?
Oh yes, "I see you baby, shaking that ass, shaking that ass, I see you baby, shaking that ass, shaking that ass!"
Is this an American board? |
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Skippy
Pocket GPS Verifier
Joined: 24/06/2003 00:22:12
Posts: 2946
Location: Escaped to the Antipodies! 36.83°S 174.75°E
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| Posted: Thu Sep 01, 2005 3:05 pm Post subject: |
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It has censored you because you got the spelling wrong. It should be arse. 
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Masked-Marauder
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| Posted: Thu Sep 01, 2005 3:08 pm Post subject: |
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| ! I never realised it was arse! |
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aengus
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Joined: Aug 31, 2005
Posts: 4
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| Posted: Thu Sep 01, 2005 4:45 pm Post subject: |
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[quote="Skippy"]
The Police have special speedos calibrated in 1 mph increments and accurate to 1 mph so don't try and suggest to them that [b]their[/b] speedo was reading fast. [/quote]
ah, but you CAN ask when their speedo was last calibrated, as this may have a bearing on possible prosecution/defense strategy.... could also P them off somewhat and remove any leeway they might have been willing to show you
regards |
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Masked-Marauder
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Joined: Aug 18, 2005
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| Posted: Thu Sep 01, 2005 6:42 pm Post subject: |
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| aengus wrote: | | Skippy wrote: |
The Police have special speedos calibrated in 1 mph increments and accurate to 1 mph so don't try and suggest to them that their speedo was reading fast. |
ah, but you CAN ask when their speedo was last calibrated, as this may have a bearing on possible prosecution/defense strategy.... could also P them off somewhat and remove any leeway they might have been willing to show you
regards |
The police will seldom if ever prosecute with evidence from a callibrated speedometer, it will most likely be VASCAR and PolicePilot both of which are calibrated at the start and end of every shift using a marked and measured mile. |
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martint123
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Joined: Jun 28, 2005
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| Posted: Thu Sep 01, 2005 11:38 pm Post subject: |
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That's if they can use a tape measure correctly :P
http://www.dailyrecord.co.uk/news/news/tm_objectid=15889033%26method=full%26siteid=66633-name_page.html
PC Hughes said he and his partner have to calibrate the device every day and had done so that morning.
He said they calibrated the machine on a stretch of road which he believed to be exactly half a mile long.
On several occasions, he and his colleague had used a 150ft length of steel tape to confirm the distance was exactly half a mile.
But he said each time the measurement had been 26.4 lengths of the steel tape RodMcKenzie, defending, told thecourt that wasnearer to three quarters of a mile, rendering the calibration totally wrong.
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Masked-Marauder
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Posts: 89
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| Posted: Fri Sep 02, 2005 1:47 pm Post subject: |
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| martint123 wrote: |
On several occasions, he and his colleague had used a 150ft length of steel tape to confirm the distance was exactly half a mile.
But he said each time the measurement had been 26.4 lengths of the steel tape RodMcKenzie, defending, told thecourt that wasnearer to three quarters of a mile, rendering the calibration totally wrong.
[/i] |
Actually the distance that 26.4 x 150 = is exactly 3/4 of a mile. |
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uk89camaro
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Joined: Jul 04, 2005
Posts: 113
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| Posted: Fri Sep 02, 2005 2:08 pm Post subject: |
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| Masked-Marauder wrote: | | tomo1340 wrote: |
I have been told that the police/speed cameras give you 10% leeway due to speedo inaccuracies, however a guy from my old work got stung in Preston twice in a few weeks doing 31mph and 32mph in a 30 zone so don't take that as gospal. |
The of Chief Police Officers (ACPO) guidelines are 10% + 2mph as the prosecution threshold, so in a 30mph zone, 34 mph no prosecution, 35mph and your ticketed.
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Warwickshire police have set all their 30 mph cameras to exactly that. I was "offered" a place on a speed awareness 1 day course...no points..but the course costs £60. No course attendance =£60+3 points. Only available for up to 34 mph offences, and some people on the course had only done 31 mph!!!!! 
And i have a bloody origin that i hadn't downloaded a new database on for a couple weeks.
Oh, and the GPS can't keep up with me a Santa Pod raceway. It's about 10 mph behind in the 1/4
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