Net Book Value shall be calculated based upon depreciation on a straight 
line basis over a 20 year period beginning on the purchase date, as set forth 
in Appendix C.  Under no circumstances shall Customer be obligated to 
reimburse or otherwise keep ENA whole with respect to, or take assignment of, 
any agreement or obligation entered into by ENA after the effective date of 
this Agreement (or any amendment of any agreement existing prior to the 
effective date of this Agreement) without Customer's prior written approval 
of such agreement or obligation.