Gross profit, defined as Net sales less Cost of products sold increased by $279 million in 2017 from 2016 and decreased by $2 million in 2016 from 2015. As a percent of sales, gross profit was 38.8% in 2017, 34.9% in 2016 and 34.4% in 2015. The 3.9 percentage-point increase in gross profit percentage in 2017 and 0.5 percentage-point increase in gross profit percentage in 2016 were due to the following factors: Margin Impact 2017 2016 Pension and postretirement benefit mark-to-market adjustments.

What does this trend suggest?