TWO men who admitted trafficking 51 kilograms of cannabis escaped with a two-year sentence after a judge got his sums wrong, it was claimed yesterday. Mr Justice Bewley wrongly calculated 51,230 grams as 5.1 kg when he jailed the pair in November, said counsel Darryl Saw. But he was not the only one. Mr Saw said he challenged colleagues to do the sum and two of the five lawyers he tested got it wrong. The gaffe was revealed as the Attorney-General demanded stiffer penalties for cannabis traffickers. He was also seeking a review of the sentences on Wong Wai-sheung and Tuen Shui-ming. They were arrested in January last year, after 192 slabs of cannabis were found in the boot of their motor vehicle. Wong, 24, a mainland farmer, was freed two days ago. Tuen, 35, a waiter, was to be released next Wednesday. But both could face stiffer terms. The Court of Appeal ordered Wong and Tuen be kept in jail until June 9 while it reconsidered their sentences. Mr Saw, for the Attorney-General, said the judge had 'quite obviously made a flagrant error'' because two years was the minimum sentence for someone caught with three to six kilograms. A transcript of the November hearing also showed that the judge had referred to the haul as five kilograms. But Mr Saw added: 'To be fair to the judge I asked five colleagues how much 51,000 grams was in kilograms. Three said 51 and two said five.' Mr Justice Litton agreed that the judge appeared to have slipped up. But Philip Dykes, counsel for Wong and Tuen, defended the two-year sentence. He said Mr Justice Bewley had not made a mistake because it was the weight of the psychoactive content which was relevant - in this case 1.174 kg. Mr Saw also called for an overall increase in penalties for cannabis trafficking as seizures had rocketed in recent years - from about 58 kg in 1988 to 3,339 kg in 1994. 'Cannabis is being used and trafficked in Hong Kong on a very regular basis as opposed to 1986 when these sentence guidelines were established,' said Mr Saw. 'Current sentencing levels are not deterring traffickers.' However, Mr Justice Mortimer said raising penalties had not seemed to work in other countries.