N.Y. Comp. Codes R. & Regs. tit. 16 § 61.5
Where return is involved or claimed, the utility shall establish by competent evidence the original cost of the property used and useful in the service to which the rates, rules and regulations involved in the proceeding relate and the accrued depreciation thereon. All property not so used and useful shall be excluded (note particularly of section 61.3[d][5] of this Part). Accrued depreciation as used herein means the loss or depletion in worth or value, compared with a specified cost new, due to all causes which bring about the ultimate retirement of the property, such as wear and tear, decay, action of the elements, inadequacy, obsolescence, changes in the art, changes in demand and requirements of public authorities. Departure from newness, estimated cost of needed repairs or that part of depreciation which may be measured by inspection alone will not be accepted as satisfactory evidence of the total amount of accrued depreciation actually existing in the property.
N.Y. Comp. Codes R. & Regs. Tit. 16 § 61.5