Advance tax estimates alone do not justify re-opening past assessments; concealed income must be assessed in its own year. Mere declaration of a substantially higher income for payment of advance tax in the current year does not, by itself, justify re-opening assessments of earlier years or initiating roving inquiries; reopening must follow established judicial principles under the statutory reopening provisions. Income concealed in an earlier year must be assessed in that year and cannot be set off against higher advance-tax estimates declared for a later year; taxpayers are advised to make full voluntary disclosure and apply to the Commissioner for reduction or waiver of penalty and interest under the statutory relief mechanism.