The Sensex at the Bombay Stock Exchange fell 23 points, or 0.1 per cent, to 17,750 in early trade on Tuesday morning, in line with weak regional bourses.But later, after swinging between the negative and positive zone, in volatile trade, the Sensex stood a moderate 33 points, or 0.2 per cent in positive territory, at 17,806 in afternoon deals, a short while ago.Other Asian markets in China, Hong Kong, Singapore and South Korea were slightly down on Tuesday, after Moody's Investors Service cut the debt ratings on six European countries, including Italy, Spain and Portugal. Moody's also said that the UK and France may be stripped of their top ratings.