ADDITIONAL FINANCIAL INFORMATION OFF-BALANCE SHEET ARRANGEMENTS 45 On December 31, 2020, we had no material off-balance sheet arrangements. Return on Invested Capital. We believe ROIC is a useful measure for investors because it reflects our ability to generate returns from the capital we have deployed in our operations. We use ROIC to evaluate investment decisions and as a performance measure in evaluating management. We define ROIC as net operating profit after taxes divided by average invested capital. Net operating profit after taxes is defined as earnings from continuing operations plus after-tax interest and amortization expense, calculated using the statutory federal income tax rate. Average invested capital is defined as the sum of the average debt and shareholders’ equity excluding accumulated other comprehensive loss. ROIC excludes goodwill impairments and non-economic accounting changes as they are not reflective of company performance. ROIC is calculated as follows: repaying maturing debt, funding business acquisitions, repurchasing our common stock and paying dividends. We use free cash flow from operations to assess the quality of our earnings and as a key performance measure in evaluating management. The following table reconciles the free cash flow from operations with net cash provided by operating activities, as classified on the Consolidated Statement of Cash Flows in Item 8: * 2017 earnings from continuing operations and 2017 and 2018 average invested capital have not been restated for the retrospective application of a change in accounting principle related to the amortization of actuarial gains and losses for our qualified U.S. government pension plans, which we adopted in the fourth quarter of 2020 as discussed in Note T to the Consolidated Financial Statements in Item 8. Year Ended December 31 2020 2019 2018 2017 2016 Net cash provided by operating activities $ 3,858  $ 2,981  $ 3,148  $ 3,876  $ 2,163  Capital expenditures (967) (987) (690) (428) (392) Free cash flow from operations $ 2,891  $ 1,994  $ 2,458  $ 3,448  $ 1,771  Cash flows as a percentage of earnings  from continuing operations: Net cash provided by operating activities 122  % 86 % 94 % 133 % 81 % Free cash flow from operations 91  % 57 % 73 % 118 % 66 % Year Ended December 31 2020 2019 2018 2017 2016 Earnings from continuing operations $ 3,167  $ 3,484  $ 3,358  $ 2,912  $ 2,679  After-tax interest expense 386  373  295  76  64  After-tax amortization expense 280  287  258  51  57  Net operating profit after taxes $ 3,833  $ 4,144  $ 3,911  $ 3,039  $ 2,800  Average invested capital $ 32,431  $ 29,620  $ 25,367  $ 18,099  $ 17,168  Return on invested capital 11.8  % 14.0 % 15.4 % 16.8 % 16.3 %