operating working capital at december 31 , 2012 increased $ 139 million compared with the prior year end level ; however , excluding the impact of currency and acquisitions , the change was a decrease of $ 21 million during the year ended december 31 , 2012 . this decrease was the net result of decreases in all components of operating working capital . trade receivables from customers , net , as a percentage of fourth quarter sales , annualized , for 2012 was 17.6% ( 17.6 % ) , down slightly from 17.9% ( 17