A motorist has been cleared of a driving charge after contesting evidence from a speed gun.
The ProLaser III speed gun
James MacGregor was clocked at 132mph on the A9 - but tests showed that the top speed of his imported Subaru had been limited to 107mph.
Campaigners want the guns withdrawn after the case was found not proven.
But Northern Constabulary said it would continue to use the equipment - and the Crown said it had "no concerns" over its accuracy.
Mr MacGregor, 34, from Dalcross, Inverness, was cleared of driving dangerously by Sheriff Alexander Pollock.
He had been accused of travelling at 132mph at Daviot on 6 August last year - almost twice the 70mph limit.
Traffic police told Inverness Sheriff Court that the ProLaser III speed gun had operated correctly when it recorded Mr MacGregor.
His car had been about 2,000ft away at 2100 GMT, as it was getting dark.
But his lawyer David Hingston produced evidence in court which proved the vehicle was a "grey import" from Japan and had been fitted with an electronic speed limiter, which is a legal requirement in the country.
Defence witness Gavin Wallace, of Aberdeen-based Wallace Per4mance, said he tested the car on a rolling road and found its top speed was 107mph. He said the Subaru had at no point been tampered with.
The court heard the car could not have reached the speed recorded
Sheriff Pollock found the case against Mr MacGregor not proven.
Afterwards, Mr Hingston said: "This has huge implications throughout Scotland and the whole of the UK.
"In this case we had a reading of 132mph from a vehicle that is not capable of doing that speed. We have proved that this so-called 100% accurate machine is unreliable.
"Everybody being stopped as a result of a ProLaser reading should now be pleading not guilty."
Paul Smith, of the Safe Speed road safety campaign, said: "We must cease all use of these devices to prosecute motorists until such time as the errors can be fully explained and confidence restored."
The website for the US-based manufacturer of the ProLaser says the gun has a range of 1,000ft - half the distance involved in the case.
No-one from the company was available for comment.
Inspector John Smith, of Northern Constabulary, said the force would not stop using the devices.
"There is nothing to suggest that the equipment does not work," he said.
A Crown Office spokesman said: "Having reviewed the circumstances of the case and spoken to senior officers of Northern Constabulary I have no concerns as to the general accuracy of Pro-Laser III equipment.
"As a matter of practice, Pro-Laser III equipment - which has been approved for use by the secretary of state - is checked for accuracy in accordance with its operating instructions and standard police procedure on every occasion before it is used."