This excerpt taken from the HILL DEF 14A filed Apr 30, 2009.
Payment of Purchase Price; Payroll Deductions
The purchase price of the shares is accumulated by payroll deductions over the offering. At any time during the offering, a participant may reduce or terminate his or her payroll deductions as the Board or Compensation Committee provides in the offering. A participant may not increase or begin such payroll deductions after the beginning of the offering except as provided for in the offering. All payroll deductions made for a participant are credited to his or her account under the Amended Purchase Plan and deposited with the our general funds. A participant may not make additional payments into such account.