HAN Cheuk-pun peered confidently into the mist and rain that descended yesterday afternoon. ''Six kilometres,'' he said, noting the figure down on his pad, before turning to gaze up into the sky. Mr Han is one of the observers working at the Royal Observatory, and six km was the visibility level at 3 pm. While predicting the weather has become a lot more precise, much still depends on being able to assess weather conditions. And for that nothing more is needed than a clear eye and good judgment. Two years of training and on-the-job experience help to provide the latter, while good eyesight is ensured by a medical check-up. The observers, from the vantage point of the roof of the Royal Observatory building in Tsim Sha Tsui, determine the visibility conditions and cloud level by using certain landmarks in the Hong Kong skyline. Mr Han explained that if the top of Central Plaza in Wan Chai was the highest point visible he would know that the cloud level was 374 metres. According to Leung Wing-mo, the Senior Scientific Officer at the station, there was little chance of the weather improving over the weekend. ''This is probably the worst time of the year to hold a fireworks display,'' he said. ''There's a maritime breeze coming in from the South China Sea, and that's what is bringing all this mist and rain.''