Section 401. When interests are valued under this article

The following
  interests shall be valued in the manner provided by this article: (a) an
  interest in real property dependent as to value upon the duration of one
  or more lives in being, whether such interest is present or future;  and
  (b)  a  future interest preceded only by one or more interests described
  in clause (a); whenever 1. the owner of such  interest  is  entitled  to
  receive  a  sum  in  gross  in  satisfaction  of, or in compensation for
  impairment of, his interest in real property which has been  transformed
  into  a  fund  by judicial action or proceeding; or 2. ownership of real
  property is divided into successive legal interests,  including  one  or
  more  interests  dependent  as to value upon the duration of one or more
  lives of persons in  being,  and  the  fraction  of  complete  ownership
  belonging  to  each partial owner must be ascertained so as to permit an
  adjudication of the fraction of some new  capital  expenditure  required
  either  for  the payment of a mortgage, special assessment or other lien
  upon such property, or for the satisfaction of an obligation imposed  by
  law  as  an incident of ownership; or 3. such valuation is necessary for
  the final determination of some action  or  proceeding,  other  than  an
  action  or  proceeding  for  which  the  insurance  law,  the  workmen's
  compensation law or the tax law prescribes methods of valuation.