Tribunal held that ; the claim for deduction towards provision for warranties made on the basis of past experience based on statistical data by adopting scientific method to fulfil contractual obligations arising out of concluded contracts of sale/services was an ascertained liability. The principles of res judicata are not applicable but the principles of consistency have to be maintained to instill certainty in tax matters in the minds of taxpayer so that they can plan their affairs unless perversity is shown in the action of a taxpayer in claiming deduction while computing income chargeable to tax or it is shown that an attempt is made by taxpayer to defraud the Revenue or an unconscionably high claim of deduction is made by the taxpayer which breaches all canon of equity, justice and law.( AY.2013-14)