This excerpt taken from the ABM 10-K filed Jan 14, 2005.
Stock-Based Compensation. The Company accounts for stock-based employee compensation plans using the intrinsic value method under the recognition and measurement principles of Accounting Principles Board (APB) Opinion No. 25, Accounting for Stock Issued to Employees. The Companys application of APB Opinion No. 25 does not result in compensation cost because the exercise price of the options is equal to the fair value of the stock at the grant date. Under the intrinsic value method, if the fair value of the stock is greater than the exercise price at grant date, the excess is amortized to compensation expense over the estimated service life of the recipient.