                                                 No. 8 5 - 8 9
                          IN THE SUPREME COURT OF THE STATE OF MONTANA
                                                      1985




IN RE THE MARRIAGE OF
KARL A. GIES,
                                  Petitioner and Respondent,


ELSIE L. GIES,
                                  Respondent and Appellant.




APPEAL FROM:                      District Court of the Tenth Judicial District,
                                  In a.nd for the County of Petroleum,
                                  The Honors-ble Peter Rapkoch, Judge presiding.
COUNSEL OF RECORD:

          For Appellant:
                                  Linda L. Harris, Billings, Montana

          For Respondent:
                                  Jon A. Oldenburg, Lewistown, Montana




                                                      Submitted on briefs: July 11, 1 9 8 5
                                                                  Decided: November 12, 1985


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                                                      Clerk
Mr. Justice William E. Hunt, Sr., delivered the Opiniorl of
the Court.


        Elsie Gies appeals from a decree of the District Court
of   the    Tenth Judicial District, Petroleum County, which
modified a child support order.
     We affirm.
        The appellant raises two issues on appeal.         The first is
whether the District Court erred in failing to partition the
parties' real property.          The second is whether the District
Court erred in changing the method by which the child support
obligation is calculated.
     As to the first issue, we hold that the doctrine of the
"law of the case" applies.        That doctrine provides that where
a decision has been         rendered by the Supreme Court on a
particular issue between the same parties in the same case,
such decision is binding on the parties and the courts and
cannot be relitigated in a subsequent appeal.            Belgrade State
Bank v. Swainson (1978), 176 Mont. 444, 446, 578 P.2d 1166,
1-167. This case was before this Court last year in In re the
Jqarriage of Gies       (Mont. 1984), 681 P.2d      1092, 41 St.Rep.
1028.      That appeal resulted in an affirmance of the District
Court's finding that partition of the parties' real property
would produce hard feelings and adversely affect salabj.1-ity
of property.      Gies, 681 P.2d at 1093.         We hold the first
issue raised by appellant falls within the doctrine of the
law of the case and we do not address that issue.
     The     second     issue,   regarding   modification      of   child
support, does raise new matter, and requires a brief factual
discussion.       The    District   Court    dissolved   the    parties'
marriage by      decree entered April        15, 1980.      The decree
incorporated the settlement agreement of the parties, which
provided for child support as follows:
       The Petitioner [Karl] shall pay to the Respondent
       TElsie] the sum of $150.00 a month, for each child,
       until such time as each child becomes of legal age,
       marries or is otherwise emancipated.
       The Petitioner shall also pay the Respondent an
       additional 10% in each child's support, commencing
       Zanuary 1, 1981, and each year thereafter, to cover
       the inflationary cost of living for each child.
       The additional 10% cost of living shall be
       terminated when each child becomes of legal age,
       marries or is otherwise emancipated.           This
       additional sum shall also cease if inflation ceases
       in our economy or if the United States enters a
       period of depressi.on.
    After paying the support obligation for the years 1980
through 1984, Karl Gies petitioned the District Court to
amend and modify the decree and dissolution.
    The District Court in its findings of fact, found:
       4.     That said child      support provision is
       unreasonably vague, undefined and unascertainable,
       in that there is no objective criterion prescribed,
       Sy  which to measure the fact or a-mount of
       inflation, deflation or depression and it is
       therefore impossible to determine the amount of
       child support required to be paid by the Petitioner
       to the Respondent at any particular time.
        6. That it is generally accepted and the Court
        hereby takes judicial notice of the fact that
        inflation has decreased below the rate of inflation
        in existence at the time of the Decree.
Based upon its findings of fact, the Court concluded:
       3. That the provisions of the Settlement Agreement
       of the parties and therefore the Decree heretofore
       entered no longer apply with reasonableness and
       justice to the situation and circumstances of the
       parties herein and should. therefore be amended   ..
       4. That the level of child support of the payment
       of which the Petitioner is obligated should be
       changed to the sum of $300.00 per month, being
       $150.00 per month per child, the amount thereof to
       be increased or decreased according to the rate of
       inflation from that point, according to the United
       States Department of Labor Consumer Price Index, as
       shown on January 1 of each year.
          On the issue of modification of child support, this
Court will reverse the District Court only if the findings of
the District Court are clearly erroneous in light of the
evidence in the record.            Johnson v. Johnson (~ont.1983), 667


         The relevant statute is 40-4-208, MCA.                  That statute
provides :
               (1) ...   a decree may be modified by a court as to
               maintenance or support only as to installments
               accruing subsequent to the motion for modification.
               (2)(b)   Whenever    the   decree    proposed    for
               modification contains provisions       relating to
               maintenance   or    support,   modification    under
               subsection (1) may only be made:
               (i)      upon a showing of changed circumstances so
               substantial and continuing as to make the terms
               unconscionable     ....
         The     District    Court's decision does           not violate    the
statute.          First, the       ruling   is prospective only.            The
decision makes no attempt to modify payments already made by
petitioner for the years 1981 through 1984, but only affects
payments accruing subsequent to the motion for modification.
          Second, the decision is based upon a substantial and
continuing change of circumstances.               The inflation provision
of       the   decree     invites disagreement and           confusion.     The
District Court judge recognized this when he found that the
provision          was      "unreasonably       vague,       undefined,     and
unascertainable," and that it was "impossible to determine
the amount of child support to be paid by the Petitioner                    ..
..   "    By tying the increase in support to the Consumer Price
Index, the          District Court      judge    clarified      a   vague   and
troublesome provision.
          This    Court     has   recognized    that     a   modification    is
warranted         to   clarify    a vague provision that has become
unworkable.     In In re the Marriage of Smith and Smith (Mont.
1984),    692   P.2d    1221,   41   St.Rep          2325,                  the            original
dissolution decree granted the husband reasonable visitation
rights.      The   parties   continually        disagreed                      as          to   what
constituted     reasonable   visitation.                 The          District                  Court
clarified the provision by defining reasonable visitation as
every other weekend from 4:00 p.m. Friday through 8:00 p.m.
Sunday.   We affirmed the modification.
      Although that case dealt with visitation and the case at
bar deals with support, the two cases are analogous.                                        When a
provision becomes vague and unenforceable, the District Court
has   the power    to   clarify the provision so long as the
intention of the parties is given effect.                             Here, the base
amount of support remains unchanged at $300.00 per month.
The parties intended the inflation provisions "to cover the
inflationary cost of living for each child."                                The effect of
the new provision       is to clarify the ambiguous inflation
component of Karl's obligation, and to clearly establish a
level of support which covers the inflationary cost of living
for each child.    We find no error.
      Affirmed.

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