Indian equity benchmarks Sensex and Nifty50 are likely to start the October 12 session on a negative note tracking weakness across global markets. Nifty futures trading on Singapore Exchange -- an early indicator of NSE's Nifty50 index -- were last seen trading down 83.5 points or half a percent at 17,877.5 ahead of the opening of the Indian market. Equities in other Asian markets dropped and the safe-haven dollar held firm on Tuesday, as a global energy crunch fuelled inflation fears.