The following article may cast light on this issue
now I always thought that 4 out of 20 was 20%, and that 80% of 236 was 188.8 not 173. silly me...should have done my maths study at a Thai school eh? I obviously should have studied science at the military school as well, as they seem to be able to work the machines which dont work anywhere else.....Bomb detectors fail test
By The Nation
Prime Minister Ahbisit Vejjajiva said Tuesday that the controversial GT200 bomb detectors have been able to detect only four out of 20 explosives in scientific tests conducted by Science Ministry.
The result show that it would be therefore very risky to use the detectors.
"We won't buy any more GT200 bomb detectors as they do not work. It would be very risky to use them as, of the 20 tests conducted, results were achieved with only four, or just 25 per cent," the prime minister said.
The Science Ministry conducted the tests on the devices over the weekend.
The tests were undertaken at the Sirindhorn Science facility within the Thailand Science Park in Pathum Thani. Five rounds of tests were undertaken without problems before noon with another 20 rounds carried out by evening, as required by the testing committee. The test results for all 20 detectors have been stored in a deposit box for later analysis by the committee.
The prime objective of the test was to ascertain the device's efficacy with results reported to the Cabinet meeting on Tuesday. The GT200 devices tested were those used by police and military units in the South.
Earlier, senior military ordnance officers and bomb-disposal personnel briefed the Cabinet and insisted that the GT200 was "sufficiently efficient". They said it had detected explosives, weapons and narcotics in 173 out of 236 incidences.
"The success rate is higher than 80 per cent - beyond the minimum efficiency rate required," they said.
but the best bit of all - they are surprised by the result.
none of which work. 
Pete 
