Speed Measures
Discussion
Glassman said:
98.5% of speedometers are analogue. Those who break regulated speed limits can be convicted based on evidence that is digital.
A navigation system can show +/- 5-10mph when compared to a speedo.
Isn't there enough of a reasonable doubt for a landmark case?
Using them in the first place would be more realistic perhaps.A navigation system can show +/- 5-10mph when compared to a speedo.
Isn't there enough of a reasonable doubt for a landmark case?
Enough reasonable doubt for a landmark case? You are having a laugh.
I would have thought, in the unlikely event of such as case ever getting to court, that it would go against the driver.
That is, BiB & CPS allege, say 90mph recorded on their calibrated LTI 20-20, VASCAR or whatever.
Driver claims, my speedo is inaccurate, it was reading 100mph, therefore (somehow
) I must be not guilty.
CPS has a quick think, and voilà, they up the charge to 100mph. So, although they only have evidence of 90mph, they argue the intent by the driver was to do 100mph......
That is, BiB & CPS allege, say 90mph recorded on their calibrated LTI 20-20, VASCAR or whatever.
Driver claims, my speedo is inaccurate, it was reading 100mph, therefore (somehow
) I must be not guilty.CPS has a quick think, and voilà, they up the charge to 100mph. So, although they only have evidence of 90mph, they argue the intent by the driver was to do 100mph......
Glassman said:
Santa Claws said:
Speedos over-read, not under read.
If someone was pulled for 90 on a motorway, chances are their speedo was probably closer to 100.
Always over read? If someone was pulled for 90 on a motorway, chances are their speedo was probably closer to 100.
Most speedo devices in cars are inherently inaccurate at higher speeds, over reading by as much as 10% in some older cars.
Santa Claws said:
Glassman said:
Santa Claws said:
Speedos over-read, not under read.
If someone was pulled for 90 on a motorway, chances are their speedo was probably closer to 100.
Always over read? If someone was pulled for 90 on a motorway, chances are their speedo was probably closer to 100.
Most speedo devices in cars are inherently inaccurate at higher speeds, over reading by as much as 10% in some older cars.
Glassman said:
Santa Claws said:
Glassman said:
Santa Claws said:
Speedos over-read, not under read.
If someone was pulled for 90 on a motorway, chances are their speedo was probably closer to 100.
Always over read? If someone was pulled for 90 on a motorway, chances are their speedo was probably closer to 100.
Most speedo devices in cars are inherently inaccurate at higher speeds, over reading by as much as 10% in some older cars.
shack55 said:
Glassman said:
Santa Claws said:
Glassman said:
Santa Claws said:
Speedos over-read, not under read.
If someone was pulled for 90 on a motorway, chances are their speedo was probably closer to 100.
Always over read? If someone was pulled for 90 on a motorway, chances are their speedo was probably closer to 100.
Most speedo devices in cars are inherently inaccurate at higher speeds, over reading by as much as 10% in some older cars.
shack55 said:
Glassman said:
Santa Claws said:
Glassman said:
Santa Claws said:
Speedos over-read, not under read.
If someone was pulled for 90 on a motorway, chances are their speedo was probably closer to 100.
Always over read? If someone was pulled for 90 on a motorway, chances are their speedo was probably closer to 100.
Most speedo devices in cars are inherently inaccurate at higher speeds, over reading by as much as 10% in some older cars.
Secondly and more fundamentally, if you are doing 40 in a 30 it does not matter whether your speedo says 40, 33, 30, or indeed zero or 200...
You are still guilty - speeding is an absolute offence. If you found that only after you were stopped for speeding that your speedo was grossly underreading for some reason which you had no control over you may be able to use this as mitigation for a lower punishment.
ol' dirty said:
surely the speedo's should be calibrated from the manufacturer to read exact speed, not plus or minus
I was looking for a flaw... as if there was one 
My suggestion was that if there was a doubt over the accuracy of the speedo reading, perhaps there was a chance of getting let off the hook. If anyone is travelling over the speed limit, there's no doubting that they were... I was trying to apply the reasonable doubt card scenario to see how that might cook things up.
:ho-hum:
Clearly. Surely the only way a landmark case would be involved is if a prosecution case was put in place for a margin over the limit whereit could be argued that it was not possible to read the speedo sufficiently accurately?
Setting aside the issue of speedos overreading by up to 10%, in order to simplify the logic let us assume that the speedo is cock-on as Citroen speedos used to be in days of the BX.
As pointed out the speedo is an analogue meter. In scientific experiments it is convention that when determining experimental error the accuracy to which an analogue meter can be read is +/- 0.5*the minor divisions on the scale. Consider that is in laboratory conditions, taking a good hard look at the meter, having eliminated parallax errors and so on.
A lot of speedos are marked in increments of 5mph, I have seen some marked at 10mph intervals, but 5mph is normal. Thus applying the same logic as experimental error means that the speedo can be accurately read to +/-2.5mph, anything more accuarte is an estimate nothing more.
This if someone were prosecuted for 31 in a 30 you may have cause for a landmark case, but in reality it will never happen will it?
By the way, Vauxhall Novas are marked in increments of 10mph , and our Octavia VRS's are marked in major increments of 20 mph above 80.
Hope that helps
FiF
Setting aside the issue of speedos overreading by up to 10%, in order to simplify the logic let us assume that the speedo is cock-on as Citroen speedos used to be in days of the BX.
As pointed out the speedo is an analogue meter. In scientific experiments it is convention that when determining experimental error the accuracy to which an analogue meter can be read is +/- 0.5*the minor divisions on the scale. Consider that is in laboratory conditions, taking a good hard look at the meter, having eliminated parallax errors and so on.
A lot of speedos are marked in increments of 5mph, I have seen some marked at 10mph intervals, but 5mph is normal. Thus applying the same logic as experimental error means that the speedo can be accurately read to +/-2.5mph, anything more accuarte is an estimate nothing more.
This if someone were prosecuted for 31 in a 30 you may have cause for a landmark case, but in reality it will never happen will it?
By the way, Vauxhall Novas are marked in increments of 10mph , and our Octavia VRS's are marked in major increments of 20 mph above 80.
Hope that helps
FiF
minimac said:
Best way of calibrating the thing? Expensive?
What would be the point in calibrating to a higher accuracy, apart from satifying any OCD tendancies?Seriously though it changes as your tyres wear, as your wheels will need more revolutions to travel the same distance and even this would affect the accuracy!
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