law: Indian Stamp Act, 1899 
  25. Valuation in case of annuity, etc. 
  Where an instrument is executed to secure the payment of an
  
  annuity or other sum payable periodically, or where the consideration for a
  
  conveyance is an annuity or other sum payable periodically, the amount secured
  
  by such instrument or the consideration for such conveyance, as the case may
  
  be, shall, for the purposes of this Act be deemed to be- 
  (a) where the sum is payable for a definite period so that the
  
  total amount to be paid can be previously ascertained-such total amount;
  (b) where the sum is payable in perpetuity or for an indefinite
  
  time not terminable with any life in being at the date of such instrument or
  
  conveyance-the total amount which, according to the terms of such instrument or
  
  conveyance, will or may be payable during the period of twenty years calculated
  
  from the date on which the first payment becomes due; and
  (c) where the sum is payable for an indefinite time terminable
  
  with any life in being at the date of such instrument or conveyance-the maximum
  
  amount which will or may be payable as aforesaid during the period of twelve
  
  years calculated from the date on which the first payment becomes due.