Rate of depricaition

sir.. i want to know that whether it is mandatory for a private limited company to charge depreciation as per companies act,1956 in its books of accounts ?? and when i was seen the audited balance sheet for the F.Y 2012-13 on tax audited balance sheet, differed tax was not calculated and deprecation as per IT Act was carry to (Same amount as in B/S)in Books. whether it is correct ??? Plz Reply...