N.J. Stat. § 54:4-2.45
The true value of taxable tangible personal property used in business owned by a taxpayer shall be presumed to be the original cost of such property less depreciation as of the assessment date, as shown by the books and records of the person assessed, provided that the true value of depreciable property shall, so long as such property remains in use or is held for use, be presumed to be not less than 20% of its original cost. Where it is impracticable with respect to items of like property, held by the taxpayer in more than one taxing district, to maintain cost records which account separately for each such item of such depreciable property or to assess each item separately, the taxpayer may maintain its costs, value and depreciation records relative to such property by averaging in group or composite accounts. The Director of the Division of Taxation may promulgate uniform rules and regulations for the determination and reporting of costs, depreciation and values of subject property as he may find necessary to provide for fair and equal assessments.
N.J.S. § 54:4-2.45