THE Post Office has spent an extra $15.6 million - because some government mail can't be read by a mechanised sorting system. The Post Office spent $12 million on a Mechanised Letter Sorting System (MLSS) to cut costs by shedding 309 jobs over five years. But when the Postmaster-General asked the Registration and Electoral Commission to change the format and material for poll cards, he was told that suitable paper was not available in Hongkong. The Post Office tracked down a supplier themselves, only to find that the government printer had already ordered the paper. But Mr Chan Yuk-lun, senior executive officer of the Registration and Electoral Office, has admitted his office is still discussing the issue with the Government. Although the Government had identified suitable paper which could be read by the computer, it did not fit the printing machine, he said. Under the new system, it was expected that most letters could be machine-read using Optical Character Recognition (OCR) or video coding which required addresses to be printed in a special format. It was estimated that half the letters could be handled by OCR and 40 per cent by video coding, with only 10 per cent left for manual sorting, a job which occupies 80 per cent of the Post Office's 5,400 workers each year. But Mr Jenney said the actual amount of coded mail failed to reach the estimates. Only 43.8 per cent of mail in 1991-92 was OCR-coded and 22.6 per cent was video-coded, leaving 33.6 per cent - more than three times the expected level - to be sorted by hand. One reason for the shortfall was an unco-operative attitude from some government departments, the report said. Despite efforts by the Postmaster-General to convince government departments to adapt their mail, Mr Jenney said: ''The pace at which major user departments have adapted their mail to the MLSS requirement compatibility varies.'' He cited the City and New Territories Administration and the Registration and Electoral Office as examples. In 1991, a total of 12 million items were mailed by the two departments, mainly poll cards and publicity material. The election material had average OCR-coded rates of only 30 to 40 per cent, largely due to the thickness of poll cards being incompatible to the format. Another reason cited by Mr Jenney was a lack of incentive for bulk mailers to use special ink and paper to make letters readable by the machine.