ANALOG DEVICES, INC. NOTES TO CONSOLIDATED FINANCIAL STATEMENTS — (Continued) As of November 2, 2019, a total of 10.2 million and 1.4 million common shares were available for future grant under the 2006 Plan and 2010 Plan, respectively, and 21.2 million common shares were reserved for issuance under the 2006 Plan, 2010 Plan and the Company's previous equity compensation plans. Stock-based compensation is measured at the grant date based on the grant-date fair value of the awards ultimately expected to vest and is recognized as an expense on a straight-line basis over the vesting period. Determining the amount of stock-based compensation to be recorded requires the Company to develop estimates used in calculating the grant-date fair value of stock options. In connection with the Acquisition, the Company issued equity awards, consisting of restricted stock awards and restricted stock units (replacement awards), to certain Linear employees in replacement of Linear equity awards. The replacement awards consisted of restricted stock awards and restricted stock units for approximately 2.8 million shares of the Company's common stock with a weighted average grant date fair value of $82.20. The terms and intrinsic value of these replacement awards are substantially the same as the converted Linear awards. The fair value of the replacement awards associated with services rendered through the Acquisition Date was recognized as a component of the total acquisition consideration, and the remaining fair value of the replacement awards associated with post-Acquisition services will be recognized as an expense on a straight-line basis over the remaining vesting period. The Company has, from time to time, modified the terms of its equity awards to employees and directors. The modifications made to the Company’s equity awards in fiscal 2019, fiscal 2018 and fiscal 2017 did not result in significant incremental compensation costs, either individually or in the aggregate. The Company uses the Black-Scholes valuation model to calculate the grant-date fair value of stock option awards. The use of valuation models requires the Company to make estimates and assumptions, such as expected volatility, expected term, risk-free interest rate, expected dividend yield and forfeiture rates. The grant-date fair value of restricted stock units with a service condition represents the value of the Company's common stock on the date of grant, reduced by the present value of dividends expected to be paid on the Company's common stock prior to vesting. Information pertaining to the Company’s stock option awards and the related estimated weighted-average assumptions to calculate the fair value of stock options using the Black-Scholes valuation model granted in fiscal 2018, fiscal 2017 and fiscal 2016 is as follows:  Linear Replacement Awards Modification of Awards Grant-Date Fair Value Expected volatility  — The Company is responsible for estimating volatility and has considered a number of factors, including third-party estimates. The Company currently believes that the exclusive use of implied volatility results in the best estimate of the grant-date fair value of employee stock options because it reflects the market’s current expectations of future volatility. In evaluating the appropriateness of exclusively relying on implied volatility, the Company concluded that: (1) options in the Company’s common stock are actively traded with sufficient volume on several exchanges; (2) the market prices of both the traded options and the underlying shares are measured at a similar point in time to each other and on a date close to the grant date of the employee share options; (3) the traded options have exercise prices that are both near-the-money and close to the exercise price of the employee share options; and (4) the remaining maturities of the traded options used to estimate volatility are at least one year. Stock Options 2019 2018 2017 Options granted (in thousands) 454  603  1,480  Weighted-average exercise price $107.11 $90.98 $82.99 Weighted-average grant-date fair value $23.29  $20.82  $17.12  Assumptions: Weighted-average expected volatility 26.4  % 27.7  % 26.4  % Weighted-average expected term (in years) 5.0 5.0 5.1 Weighted-average risk-free interest rate 2.4  % 2.6  % 2.1  % Weighted-average expected dividend yield 2.0 % 2.1 % 2.2 % 70