"In terms of differentials (to London levels), the change is not much. But offers have dropped by some $100 and could drop even more," a trader at a western trading firm said. Offers for Vietnam's robusta grade 2, five per cent black and broken were offered at around $1,500 a tonne, down from around $1,600 late last week. "I heard some small deals were done at around $1,470 on Wednesday," another trader said.