NEW DELHI: Software services maker Persistent Systems shares plunged as much as 16.5 per cent to Rs 552, their lowest level since July 2014.The stock posted its biggest daily percentage loss since February 2.The Q2 profit rose marginally to Rs 881 million($12.02 million), the company said on Sunday.Mix shift to offshore, project closures in quarter and lumpiness of IBM reseller revenues led to weak performance, revenue was flat in dollar terms.Morgan Stanley analysts say weak execution and disappointing revenue growth were key negatives in the quarter, partially offset by better margin performance.More than 733,926 shares traded as of 0432 GMT, 3.3 times their 30-day average of 231,879.Up to Friday's close, stock had fallen nearly eight per cent so far this year