Table:
|  | 2019 | 2018 | 2017 |
| --- | --- | --- | --- |
| Risk-free interest rate | 2.68% | 1.74%-1.94% | 0.94%-2.14% |
| Expected life (in years) | 5 | 5 | 5 |
| Expected volatility | 32.42% | 32.42% - 32.84% | 35.25%-40.22% |
| Weighted average grant date fair value | $4.72 | $3.36 | $3.69 |
Paragraphs:
Stock-Settled Stock Appreciation Rights
Stock-Settled Appreciation Rights (“SSARs”) are rights granted to an employee to receive value equal to the difference in the price of our common shares on the date of the grant and on the date of exercise. This value is settled only in common shares of Agilysys.
We use a Black-Scholes-Merton option pricing model to estimate the fair value of SSARs. The following table summarizes the principal assumptions utilized in valuing SSARs granted in fiscal 2019, 2018 and 2017:
The risk-free interest rate is based on the yield of a zero coupon U.S. Treasury bond whose maturity period approximates the expected life of the SSARs. The expected life is estimated using historical data representing the period of time the awards are expected to be outstanding. The estimated fair value of the SSARs granted is recognized over the vesting period of the awards utilizing the graded vesting method. Under this method, the compensation cost related to unvested amounts begins to be recognized as of the grant date.
Question:
Which model is used for estimating the fair value of SSARs?