We have a stock plan (the “Stock Plan”) for equity awards to eligible service providers and an inducement stock plan for newly hired employees (the “Inducement Plan”) (collectively the “Plans”). We stopped using the Inducement Plan in 2019, although it continues to govern outstanding awards granted under it. Under the Stock Plan, stock options may be granted with a fixed exercise price that is equivalent to the fair market value of our common stock on the date of grant. These options have a term of up to 10 years and vest over a predetermined period, generally four years. Incentive stock options granted under the Stock Plan may only be granted to our employees. The Stock Plan also allows for awards of non-qualified stock options, stock appreciation rights, restricted and unrestricted stock awards, RSUs and performance-based restricted stock units ("PSUs").

The estimated fair value of stock-based awards is recognized as compensation expense over the vesting period of the award, net of estimated forfeitures. We estimate forfeitures based on historical experience and expected future activity. The fair value of RSUs is determined based on the number of shares granted and the quoted price of our common stock on the date of grant. The fair value of PSUs is estimated at the grant date based on the fair value of each vesting tranche as calculated by a Monte Carlo simulation. The fair value of stock options is estimated at the grant date based on the fair value of each vesting tranche as calculated by the Black-Scholes-Merton (“BSM”) option-pricing model. The BSM model requires various highly judgmental assumptions including expected volatility and option life. If any of the assumptions used in the BSM model change significantly, stock-based compensation expense may differ materially in the future from that recorded in the current period. The fair values of our stock option grants were estimated with the following weighted average assumptions:

The impact on our results of operations from stock-based compensation expense was as follows (in thousands):

At September 30, 2022, total compensation cost related to stock options granted but not yet recognized, net of estimated forfeitures, was $169,706. This cost will be amortized on the straight-line method over a weighted-average period of approximately 0.9 years. The following table summarizes certain information about stock options:

The aggregate intrinsic value represents the difference between the exercise price of the underlying options and the quoted price of our common stock for the number of options exercised during the periods indicated. We issue new shares of common stock upon exercise of stock options.

At September 30, 2022, total compensation cost not yet recognized related to granted RSUs was approximately $141,416, net of estimated forfeitures. This cost will be amortized on the straight-line method over a weighted-average period of approximately 0.5 years.

In January 2021, we awarded PSUs to Messrs. Derrickson and Wheaton. The PSUs vest based on a combination of Bsquare's stock price performance and Messrs. Derrickson's and Wheaton's continued service. The first vesting measurement date was January 5, 2022 and the final measurement date is July 5, 2025. We estimated the fair value of the awards utilizing Monte Carlo simulations, and we record the expense in the selling, general and administrative line of our consolidated statement of operations. For the three months ended September 30, 2022 and 2021, we recorded expense of approximately $8,100 and $17,000, respectively. For the nine months ended September 30, 2022 and 2021, we recorded expense of approximately $29,100 and $51,000, respectively. At September 30, 2022, total compensation cost not yet recognized related to granted PSUs was approximately $30,200 and will be amortized over a weighted-average period of approximately 2.8 years.

In January 2022, the Compensation Committee of the board of directors (the "Committee") amended the PSU agreements, updating the definition of stock price performance, and reducing the total number of PSUs available to Messrs. Derrickson and Wheaton by 50,000 and 33,333 shares of common stock, respectively (the "2021 Shares"). In lieu of any claim to the 2021 Shares, each of Messrs. Derrickson and Wheaton received in February 2022 a cash settlement in an amount equal to the number of 2021 Shares multiplied by the closing price per share on January 5, 2022. Because the cash settlement was equal to the fair value of the 2021 Shares, we recognized the cash settlement as a charge to equity in the amount paid to repurchase the 2021 Shares.

The following table summarizes our shares of common stock reserved for future issuance under the Plans as of September 30, 2022: