We adopted stock option plans for the benefit of our employees and outside directors. Under terms of the plans, stock options are granted at an amount less than of the quoted market price of the underlying shares at the date of grant. Stock options are exercisable for terms of to years and vest ratably over terms of to years. All of our stock option plans have been approved by our shareholders.

 

On we adopted The Mesa Laboratories, Inc. Equity Plan (the Plan”), which was subsequently approved by our shareholders on at our Annual Meeting of Shareholders. The purpose of the Plan is to promote the success and enhance the value of the Company by linking the personal interests of our employees, officers and directors to those of our shareholders by providing such persons with an incentive for outstanding performance. A total of shares of common stock were reserved for issuance under the Plan and are subject to terms as set by the Compensation Committee of the Board of Directors at the time of grant. As of we have stock options outstanding and have issued shares of restricted stock under the Plan.

Under the plan (the Plan”), a total of shares of common stock were reserved for issuance and were subject to terms as set by the Compensation Committee of the Board of Directors at the time of grant. On our shareholders approved an amendment to the Plan whereby the number of shares authorized for issuance was increased to As a result of the approval of the Plan by our shareholders, further awards will be made under the Plan and it will remain in effect only as long as awards previously made thereunder remain outstanding. As of we have stock options outstanding under the Plan. O

n we filed a Registration Statement on Form S- whereby we registered the additional shares of common stock underlying stock options issuable under the Plan.

 

Amounts recognized in the consolidated financial statements related to stock-based compensation are as follows (in thousands, except per share data):

 

 

The fair value of each option award is estimated on the date of grant using the Black-Scholes option valuation model that uses assumptions noted in the following table. We use historical data to estimate volatility, expected option life and forfeiture rate. The risk-free rate is based on the United States Treasury yield curve in effect at the time of grant. The dividend yield is calculated based upon the dividend payments made during the prior quarters as a percent of the average stock price for that period.

 

 

A summary of the option activity as of and for the years ended and is as follows:

 

A summary of the status of our unvested option shares as of and for the years ended and is as follows:

 

 

The total intrinsic value of options exercised was and for the years ended and respectively. As of there was of total unrecognized compensation expense related to unvested options. As of we have shares available for future option grants.