pre_text: Operating Income Our operating income in fiscal year 2019 increased to $241.4 million, or 10.1 percent of net sales as compared with $189.3 million, or 8.8 percent of net sales in fiscal year 2018. Excluding surcharge revenue and special items, adjusted operating margin was 12.5 percent for the fiscal year 2019 and 10.6 percent for the same period a year ago. The increase in the operating margin reflects steady demand and improved product mix coupled with operating cost improvements offset by higher selling, general and administrative expenses compared to the same period a year ago. The following presents our operating income and operating margin, in each case excluding the impact of surcharge on net sales and special items. We present and discuss these financial measures because management believes removing the impact of these items provides a more consistent and meaningful basis for comparing results of operations from period to period. See the section “Non-GAAP Financial Measures” below for further discussion of these financial measures.
table: Fiscal Year
table: ($ in millions) 2019 2018
table: Net sales $2,380.2 $2,157.7
table: Less: surcharge revenue 438.1 365.4
table: Net sales excluding surcharge revenue $1,942.1 $1,792.3
table: Operating income $241.4 $189.3
table: Special items:
table: Acquisition-related costs 1.2 —
table: Adjusted operating income excluding special items $242.6 $189.3
table: Operating margin 10.1% 8.8%
table: Adjusted operating margin excluding surcharge revenue and special items 12.5% 10.6%
question: Analyse this data from a financial earnings document. What was the change in the amount of surcharge revenue from 2018 to 2019?