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PostPosted: Sat Jan 20, 2007 19:01 
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Now - we do use this doo0-dah here.. but only if our lads and lasses out there form an unshakeable opinion that the driver is pushing the old envelope more than within reason - anjd they want to verify the margin :wink:

I stress that Co Durham's finest do not go around collecting cash for the government coffers. If we do prosecute.. then the driver can rest easy that he was copped for the right reasons .. and we will try to help him improve with a COAST lecture as well.

But this gadget as "camera operator" will no doubt verify with me .. has to be used properly. This means that if we do use this device - then we will choose a safe place to monitor and as someone once posted - we do have the "lop-sided submarine signs" :wink: , a well publicised local timetable and some signs giving adequate warning of our monitoring. We cop a few OTT who apparently fail to COAST as they fail to see our signings :roll:

But use this gadget incorrectly - and you might as well not bother. :roll: Again - I stress that Durham and North Yorks do not lurk and fire off these devices "willy nilly" on the occasions we actually use them. You have to be judged in a professional opinion to be wide of the margin of fair tolerance - and we will ensure our roads and the the road users and residents along them are both served and protected as far as we can deliver this. :wink:

But .. I know Martin :wink: - tis the old "Waily" :wink: but I think I should draw attention to this report for the sake of discussion and debate anyway. :wink: The basic facts would have to be true.. despite "journalese writing styles" :wink:

In today's Waily on page 40 .. journalists Matthew Hickley and Arthur Martin report: (By the way the experts ARE peer reviewed :wink:

Quote:

:listenup:

NEW PRESSURE TO BAN SPEED GUN AS COURT CLEARS DRIVER

The Home Office is under growing pressure to withdraw a hand held speed camera after a motorist had a fine and points quashed as "unreliable"

David Lyall refused to aaccept a ticket because he was convinced he was below the 50 mph speed limit. The magistrates agreed :shock: :? :shock: after "peer reviewed experts" :wink: said the mibile camera failed to spot a lampost which interfered with its beam.

The Lti 20 20 speed gun has been involved in a string of controversial cases quashed by the courts, yet it remains popular with police forces across the country


WHY? OK .. because the doo-dah is the recommended one to use :wink: If used correctly - it confirms a speed - and here - we will still use a certain amount of professional judgement when making a decision on the matter. Policing, enforcing a law fairly requires common sense, together with professioanl skill and experience. Nit picking does not command respect. Realistic prosecution does. :wink:

We cannot say drive as fast or as slow as you like. We say drive at the safest speed for the condition. We may allow the odd transgression so long as we judge the driver was safe.. but we will always stress and reinforce and consolidate COAST principles just the same.


The Waily pat itself on the back a bit as it refers to some investigation its own journalists completed two years ago

I will confirm that the description of how this doo-dah works is correct :wink: I put this in italics.



I will also re-iterate - to get an accurate reading - the device has to be used according to the manufacture's specific instruction and I cannot say the civvies employed or the village NIMBY brigade have the training required to operate this doo-dah to manufacturer specs. I do know we have specific training sessions on our patch.

Quote:

A Waily investigation two years ago exposed serious glitches in the way it measures the distance to a car. meaning it can sometimes clock the wrong vehicle or become confused by scatttered laser beams by other objects.

The camera works by sending out an infra-red beam By measuring the time it takes to bounce back - it tehn determines the vehicle's speed

However, the investigation at the time recorded a brick wall travelling at 44 mph and a bicycle at 66 mph. :yikes:

Yesterday a motoring group called on the Home Office to ditch the LTI 20 20 claiming millions had lost licences or paid unfair fines.

In this latest case - David Lyall - a 58 year old technology developmetn manager was driving his Audi A4 from Swindon to
Highworth when police or cam op targetted him on a dual carriageway with a 50 mph limit.

He received a fixed penalty notice - accusing him of driving at 59 mph

Mr Lyall refused the penalty and battled in the courts for almost two years. :roll:

He was cleared at Devizes Magistrates' Courts when exper Dr Michael Clark - an expert on speed cameras (and possibly a good ally and source for you Paul :wink: ) reviewed the tape and concluded that Mr Lyall was wrongly convicted.

The magistrates said they were unhappy with the evidence as "a lamp post was in the way".

They also questioned the speed gun's ability to detect innaccurate readings known as "error trapping"


I stress that where we use this device here.. we are aware of potential fails and we will not prosecute if we conclude a rogue reading. Our guys out there receive correct training on our "weapons". I cannot vouch for others - especially those who rely on a civilian input -given the apparent controversy backed by case law.

Dr Clark in the Waily wrote:

It was a landmark ruling. The court was unhappy with the error trapping device which did not kick in when it was supposed to. Mt Lyall was not driving above the speed limit. I believe there are thousands of motorists out there who have been wrongly caught out.


Mr Lyall in the Waily wrote:

The time has come for these speed cameras to be withdrawn and all cases involving this device reviewed


ABD member Paul Gibbs wrote:

This device should be withdrawn immediately. We are not opposed to speed enforcement, but it has to be done [i] accurately


The last thing anyone wants is for innocent drivers to be prosecuted for speeding. Alll that does is form a wedge between the police and the public


I do so agree - else it undermines COAST and justice itself as well as our relationship with our public. It is a device which requires professional training and skill. It is not a device for civilians and cheapskate practices to ensure road safety.

Waily wrote:

A spokesman for Tele Traffic - which manufactures the speed guin said the Home Office had approved it after thousands of tests.

The Home Office stated it was satisfied that that all currently type approved speed meters merit their type approved status


But only if used according to manufacturer's specification based on their tests. If used incorrectly - then the device and justice become undermined.

As almost all roads have lamp posts.. then care has to be taken when aiming the device at the vehicle we think was OTT speeding. We also know more or less if we get a rogue reading and if we do so.. then we will not prosecute on the basis this would be unsound and open to bringing us into disrepute.

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PostPosted: Sat Jan 20, 2007 21:25 
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OK for Durham & North Yorks, but the cornucopia of cash from these devices was too good to miss, wasn't it? Who cares if a few motorists are walloped unfairly; they are a resource to be exploited, like North Sea oil. We have got our generous salaries and overtime, and pensions too; what is Justice anyway?

DO I read the SCPs correctly, yes, I think so.

Wickedness, malice, vindictiveness, and zealotry are all there in the SCPs. Its the same with the 'de-criminalised parking' scams as well, another £1 billion industry

GET THE CASH IN AT ALL COSTS !!

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PostPosted: Sun Jan 21, 2007 00:41 
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Quote:
The camera works by sending out an infra-red beam By measuring the time it takes to bounce back - it tehn determines the vehicle's speed

Not quite...
It sends out a series of beams. It measures how long each one took to get back. Because they travel at the speed of light the distance each one travelled can be worked out.
With two readings at a known time apart you can work out the speed. All the other readings have to give approximately the same speed reading or it will give an error.

Am I right?

I also believe the LTI 20/20 has been banned in Canada...?

Decriminalised parking enforcement is another system where the people who set the restrictions and enforce them also make money directly from doing so. :x

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PostPosted: Sun Jan 21, 2007 02:36 
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As I understand it the speed gun sends out a series of laser beam light pulses, 30 or so in 0.3 seconds, and the time it takes each pulse of light to travel to the target and back gives a sequence of distance measurements against time.

If these measurements were plotted on graph paper, or in Excel, as distance against time, then the slope of this line gives the speed. Of course this process is all done electronically using a "curve fitting" algorithm.

Something similar can be done in Excel, by adding a linear trend line to the series of points and then displaying the equation for the line.

It seems the process in the LTI is a bit more complicated, and it can ignore a number of measured distance points that do not fit with the straight line, called outliers. Essentially it ignores any distance measurements it doesn't like.

As it is understood, the so called special software that "ensures" the measurement is reliable just checks that the points lie on straight line, within acceptable limits. So far as I am aware there is no other way the accuracy of the measurement can be verified. If anyone knows otherwise, then please let us know.

Unfortunately there are various other ways, in particular the slip effect, which can also produce such a straight line, but give the wrong speed.

It would seem the Home Office knows this is a problem, but chooses to go on pretending it doesn't happen, so the police can go on raking in the money and dishing out the penalty points on the false pretence that it is improving road safety.

The argument that the LTI 20-20 is used to verify “the prior opinion of the operator that the vehicle was speeding” is nonsense. It would seem that there have never been any approval trials to show that an operator is adequately capable of forming such an opinion, particularly when the vehicle is several hundred metres away and travelling directly toward them. In fact I wonder if it is technical illegal to rely on such a prior opinion if there have not been any approval trials to establish that this is an adequate means for verifying the speed measurement with the speed gun.

In practice we know that it is most likely that no operator bothers to form a prior opinion, anymore than the are likely to check the alignment at the laser beam, but it would seem they just say they do to meet the requirements.

All the arguments about holding the LTI 20-20 steady are also a load of hogwash. Just try to take a sharp photograph with a hand held SLR camera fitted with a 300mm, or longer, telephoto lens at a shutter speed of 0.3 seconds and then see if you can recognise anything in the picture with all the motion blur.


Last edited by Dr L on Sun Jan 21, 2007 18:41, edited 1 time in total.

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PostPosted: Sun Jan 21, 2007 02:53 
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Or any other spreadsheet program :x
(Like OpenOffice.org :) )

Are ordinary binoculars a good example of how 'easy' it is to hold an LTI 20/20 steady?

I wouldn't like to trust the speed given by an LTI 20/20 unless I got got see all data it collected.
It's a bit like having a non-itemised phone bill or a supermarket receipt with only a total. They say the total is £X but how can you be sure without seeing the details? Except in this case your livelihood depends on the details being correct...

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PostPosted: Sun Jan 21, 2007 03:26 
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Article at: http://www.mailonsunday.co.uk/pages/liv ... ge_id=1770

and http://www.bbc.co.uk/insideout/west/

Ziltro I anticipate that when using binoculars your eyes can compensate for some of the movement. Persistence of vision only lasts about a fiftieth of a second, or so. Binoculars also make the traffic look like it is crawling along and destroy any sense of speed.

When you use a camera with a shutter speed of 0.3seconds it accumulates all the movement over that period, as does a handheld LTI laser speed gun.

The problem with the hand held LTI 20-20 is that there may not be any data, other than the number on the display at the back end of the device. When that is cleared there is no longer any permanent evidence, other than any notes that are taken.

Anyway, who is to say when the speed reading was obtained. It could have come from a previous car that they could not stop, so it would be a pity to waste such a reading, so just wait for the next motorist that happens along and pin the offence on them. Afer all the poor mug will have no way to prove that they were not speeding.

So it is not a matter of whether you like to trust the handheld LTI 20-20 without a record, since you would have no choice in the matter and there will be no other evidence you can use to prove otherwise.

I would also mention there was a time when we did not have itemised phone bills and shopping receipts, but we managed to live ok. It is, however, a different matter when it comes to speeding allegations, where there should be an effective means to corroborate such an important measurement, which could result in a driving ban and possible loss of employment.


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PostPosted: Sun Jan 21, 2007 11:41 
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We normally mount ours on a tripod to ensure no "hand shake". :wink:


Apart from the unmarkeds in the fleet (:hehe: and some spot them anyways :wink:) - presence out there is highly visible and we give plenty of warning along the road where we are using this device.

Device does work as described by Dr L and Ziltro above to "calculate speed". Canadian Forces found problems with the device and withdrew it temporarily pending further research. As far as I am aware - they are still using an older "tested and truer" device. :wink: called a :stop: "police car" .. :lol: "with a calibrated speedo." :wink:

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Drive without COAST and it's all your own fault!

A SMILE is a curve that sets everything straight (P Diller).

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Approach love and cooking with reckless abandon - but driving with a smile and a COAST calm mind.


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PostPosted: Sun Jan 21, 2007 15:13 
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The gun must be used absolutely (technically) correctly otherwise it is at significant risk of giving a false speed reading.

It is impossible to ensure proper usage of the equipment.
In many (if not all) resulting prosecutions, it is impossible to prove proper usage of the equipment.
It is usually phenomenally difficult, sometimes impossible, to prove the gun had given a false speed reading.

Use of tripods will not eliminate the risk of slip. In fact it could actually increase it – tripods will encourage a smooth sweep (unlike the faster judder caused by hand shake), perfect conditions for slip. Only use of a fixed tripod can reduce the risk of slip – but then how would the gun be aimed?


The MD of the company who supplies the device claims that, even though it is possible to get a false speed reading from a stationary surface, it is impossible to get a false reading from a moving surface. I have a video clip of Frank Garrett making that claim.

Frank Garrett is a liar!


Lamp posts will not yield a false speed reading (when sweeping past it in a direction perpendicular to it’s axis); the gun will either display the speed reading of the target surface (be it slipped), 0mph or E02/E03. The gun giving a speed reading even though such a post was swept through the field of view means that either:
a) the post was small or not reflective enough to block or reflect enough of the beam to cause an error of a sample.
b) the gun was panned fast enough such that the individual beam pulses were fired either side of the post, but not at the post (not so likely, but…..)
c) the gun was panned slow enough such that the beam pulses were blocked enough to prevent the pulses being reflected back in the correct manner. Reflections outside of the +/-40cm window will be discarded or completely gated out if the error is significantly greater. Up to 5 ‘outlying’ samples (out of the 40) can be discarded for the speed measurement to still be deemed valid (rightly so IMO). There is no indication of how many samples were discarded.

Failure of the gun to display an error when swept past a lamp post does not mean that the error trapping system did not properly activate.

I don’t know the details of the judgement, but I suspect the article was coloured by ‘journalistic interpretation’. I also suspect the alleged offender was simply the victim of slip effect.


Last edited by Steve on Tue Jan 23, 2007 01:27, edited 1 time in total.

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PostPosted: Sun Jan 21, 2007 15:20 
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Dr L wrote:
I am currently trying to help someone accused with a handheld LTI 20-20 of 90mph on a 60mph rural road. They utterly refute the allegation, but there was no video of photo evidence they can used to prove that.

The allegation is nonsense, since if he was going at that speed he couldn't have been stopped in time by the PC using the speed gun.

Really?

I concede I don't know the details of the case anywhere as near as well as you, but if what you have described is the crux of your case then I suspect it is going to have problems.

Regardless, good luck with it. Let us know how it goes.


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PostPosted: Sun Jan 21, 2007 20:49 
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Dr L wrote:
As I understand it the speed gun sends out a series of laser beam light pulses, 30 or so in 0.3 seconds,

In practice we know that it is most likely that no operator bothers to form a prior opinion, anymore than the are likely to check the alignment at the laser beam, but it would seem they just say they do to meet the requirements.



i would have loved to have faced yourself in court

Quote:
Dr L

The problem with the hand held LTI 20-20 is that there may not be any data, other than the number on the display at the back end of the device. When that is cleared there is no longer any permanent evidence, other than any notes that are taken.

Anyway, who is to say when the speed reading was obtained. It could have come from a previous car that they could not stop, so it would be a pity to waste such a reading, so just wait for the next motorist that happens along and pin the offence on them. Afer all the poor mug will have no way to prove that they were not speeding.

So it is not a matter of whether you like to trust the handheld LTI 20-20 without a record, since you would have no choice in the matter and there will be no other evidence you can use to prove otherwise.


i know lets get 10 plod on the road, each with a video recording each others actions

1st we have the van mounted camera, the tape is always doctored to suit the prosecution

now we have this theory that plod record the chav who does not stop (failure to stop under the directions of a constable in uniform) so the stop the little old lady on her way home from tesco and book her instead

is this how your lads work Ingear ?

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PostPosted: Sun Jan 21, 2007 21:09 
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In Gear wrote:


But this gadget as "camera operator" will no doubt verify with me .. has to be used properly. This means that if we do use this device - then we will choose a safe place to monitor and as someone once posted - we do have the "lop-sided submarine signs" :wink: , a well publicised local timetable and some signs giving adequate warning of our monitoring.

I will also re-iterate - to get an accurate reading - the device has to be used according to the manufacture's specific instruction and I cannot say the civvies employed or the village NIMBY brigade have the training required to operate this doo-dah to manufacturer specs. I do know we have specific training sessions on our patch.



of course it has to be set up correctly and used correctly, everything is on tape fot the AKA to view

as for the training i went on the course at TT with civvy and police same course same exam, village NIMBY brigade agreed, has our mentioned expert been trained in correct procedure ?

as for the case in question i have not read enough about it, i have my views / suspicions but thats all they are

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PostPosted: Sun Jan 21, 2007 22:54 
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camera operator, if the speed gun had been on a tripod and there had been a video, or even a photo record, then the allegation may have had some credibility.

It would seem that laser camera operators have been brainwashed into believing they have an infallible measuring instrument, which would seem to be about as reliable as a tape measure made of elastic. So far as I can see camera operators are parasites on society, taking money from perfectly safe motorists going about their business as lawfully as they reasonably can. It would seem that the camera operators are not doing a jot toward improving road safety, but are keeping themselves in a well paid job at the expense of motorists.

At last some Magistrates and even a Crown court have started to recognise the unreliability of the LTI 20-20.

In my case the police manipulated the video tape when the Information Commissioner's Office forced them to provide it, then persisted in denying this until forced to investigate the matter by the Independent Police Complaints Commission, when they finally owned up to the mal-practice. So as far as I can see the police will try anything they can to get speeding convictions by any means they can.


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PostPosted: Sun Jan 21, 2007 23:30 
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Many modern camcorders capture some near-IR sources as visible, in order to improve low-light performance. Try pointing one at your TV remote when pushing a button and you'll see what I mean.

What would be very interesting would be to position such a camcorder at a talivan site, recording into it's 'beaten zone' with a view to capturing scatter from approaching vehicles which would belie the aiming point of the laser.

It would not surprise me to see a jittery aim point potentially some distance from the intended.

A very coarse measurement technique, notwithstanding the ability to slow the clip and make measurements, but potentially very telling.


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PostPosted: Mon Jan 22, 2007 00:02 
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I also believe that the laser beam should be visible to the camera used (possibly using two cameras) as this is also very important data which is being thrown away.

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PostPosted: Mon Jan 22, 2007 01:29 
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The wavelength of the beam is indeed visible to typical CCD/CMOS imagers; however, even with the high power output the average energy output (for each captured frame) is extremely small, much less than a typical remote control, even with the laser set to run at max power.

Think of it like this: take your IR remote control and point it as a wall such that the beam is 30cm wide (representing 100m range). Divide that intensity by around 20 (minimum) for representative intensity – dodgy! Then add daylight to the equation – the beam won’t show up at all!

It gets worse when you consider the reduced exposure time of the imager which, in daytime conditions, will likely result with it missing the short pulses altogether because they are not in synch.

In short: it doesn’t work if there is even a hint of daylight; even during the night you will only see a return from a retro reflective surface, which is not much use unless your imager is exactly in the path of the beam; even then such a surface is small on a typical vehicle so won’t tell you much anyway – I know, I’ve tried it.


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PostPosted: Mon Jan 22, 2007 02:52 
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Hmmm, I see.

How about an imager tuned specifically to the laser wavelength, with a high framerate? I know the sun produces pretty much all em wavelengths to some degree, but on an overcast day I imagine the near-IR won't be making it through the clouds.


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PostPosted: Mon Jan 22, 2007 05:22 
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I want to say "there must be a way to see/record it, otherwise how does the device do it?" but that sounds too obvious and I must be missing something... :)

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PostPosted: Mon Jan 22, 2007 05:32 
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Ziltro wrote:
I want to say "there must be a way to see/record it, otherwise how does the device do it?" but that sounds too obvious and I must be missing something... :)


The laser pulses are very bright, but very very very short. The detector is optimised to see the fast 'rising edges' of these short pulses.

But most devices accumlate light energy over time (applies to film and video devices). The laser speed meter pulses are so very short that there's very very little total energy in them. It's like having a shutter speed that's so fast that the film doesn't get significantly exposed at all.

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PostPosted: Mon Jan 22, 2007 09:54 
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SafeSpeed wrote:
Ziltro wrote:
I want to say "there must be a way to see/record it, otherwise how does the device do it?" but that sounds too obvious and I must be missing something... :)


The laser pulses are very bright, but very very very short. The detector is optimised to see the fast 'rising edges' of these short pulses.

But most devices accumlate light energy over time (applies to film and video devices). The laser speed meter pulses are so very short that there's very very little total energy in them. It's like having a shutter speed that's so fast that the film doesn't get significantly exposed at all.

:yesyes:
Additionally, photodiode based imagers are quite insensitive compared to avalanche diodes (when biased right); more significantly their response time are also phenomenally fast - ideally suited for picking the up fast edges.

Some numbers:
Laser pulse power: 34W (yes, really)
Laser pulse length: 12ns
Laser repetition rate: 8ms (extremely low duty cycle)

A high frame rate recorder should help, but I reckon the imager will still be far too slow to be of any real use.


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PostPosted: Mon Jan 22, 2007 11:09 
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It would be better if all of the distance data points measured by the gun were stored on the tape. The data could then be analysed later to find out what went wrong in these disputed cases.

We use this technique a lot to find out what is wrong with machines I work on. The values captured by the equipment are always recorded accurately, but that does not mean the values are correct (or what you expect)! Once you have the data you can analyse it to understand what is really happening and why the data appears incorrect. Throwing away 'inconvenient' data is a really bad idea until you have understood what caused it.


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