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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13G

                    Under the Securities Exchange Act of 1934
                                (Amendment No.*)


                                (Name of Issuer)
TRIMBLE NAVIGATION LTD

                         (Title of Class of Securities)
COMMON STOCK

                                 (CUSIP Number)
896239100

             (Date of Event Which Requires Filing of this Statement)

December 31, 1999

Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

                               [_x_] Rule 13d-1(b)
                               [___] Rule 13d-1(c)
                               [___] Rule 13d-1(d)


* The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).

Potential persons who are to respond to the collection of information contained
in this form are not required to respond unless the form displays a currently
valid OMB control number.


SEC 1745 (3-98)                                                Page   of   pages

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CUSIP No.                                                     Page   of   Pages
896239100

--------------------------------------------------------------------------------
1    NAME OF REPORTING PERSONS
     IRS IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
FRONTIER CAPITAL MANAGEMENT CO., INC.

--------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (See Instructions)
     (a) [  ]
     (b) [  ]
--------------------------------------------------------------------------------
3    SEC USE ONLY

--------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION
DELEWARE

--------------------------------------------------------------------------------
          NUMBER OF         5     SOLE VOTING POWER 1,313,730
           SHARES
        BENEFICIALLY        ----------------------------------------------------
          OWNED BY          6     SHARED VOTING POWER 
           EACH
         REPORTING          ----------------------------------------------------
           PERSON           7     SOLE DISPOSITIVE POWER 1,313,730
            WITH
                            ----------------------------------------------------
                            8     SHARED DISPOSITIVE POWER

--------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
1,313,730
--------------------------------------------------------------------------------
10   CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES 
     (See Instructions)

--------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
5.83%
--------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON (See Instructions)
IA
--------------------------------------------------------------------------------





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CUSIP No.                         13G                          Page   of   Pages
896239100

ITEM 1.

     (a)  Name of Issuer:
TRIMBLE NAVIGATION LTD

     (b)  Address of Issuer's Principal Executive Offices:
645 NORTH MARY AVENUE
POST OFFICE BOX 3647
SUNNYVALE, CA 94088

ITEM 2.

     (a)  Name of Person Filing:
FRONTIER CAPITAL MANAGEMENT LLC.

     (b)  Address of Principal Business Office:
99 SUMMER STREET, BOSTON, MA 02110

     (c)  Citizenship:
DELAWARE

     (d)  Title of Class of Securities:
COMMON STOCKS

     (e)  CUSIP Number:
896239100



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CUSIP No.                           13G                       Page   of   Pages
896239100

ITEM 3.   If this statement is filed pursuant to rule 240.13d-1(b) or 
          240.13d-2(b) or (c), check whether the person filing is a:

          (a)  [  ] Broker or dealer registered under section 15 of the Act (15
                    U.S.C. 78o).

          (b)  [  ] Bank as defined in section 3(a)(6) of the Act 
                    (15 U.S.C. 78c).

          (c)  [  ] Insurance company as defined in section 3(a)(19) of the Act
                    (15 U.S.C. 78c).

          (d)  [  ] Investment company registered under section 8 of the 
                    Investment Company Act of 1940 (15 U.S.C. 80a-8).

          (e)  [X]  An investment adviser in accordance with 
                    240.13d-1(b)(1)(ii)(E).

          (f)  [  ] An employee benefit plan or endowment fund in accordance 
                    with 240.13d-1(b)(1)(ii)(F).

          (g)  [  ] A parent holding company or control person in accordance
                    with 240.13d-1(b)(1)(ii)(G)

          (h)  [  ] A savings association as defined in section 3(b) of the 
                    Federal Deposit Insurance Act (12 U.S.C. 1813).

          (i)  [  ] A church plan that is excluded from the definition of an
                    investment company under section 3(c)(14) of the Investment
                    Company Act of 1940 (15 U.S.C. 80a-3).

          (j)  [  ] Group, in accordance with section 240.13d-1(b)(1)(ii)(J)






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CUSIP No.                  13G                       Page   of   Pages
896239100

ITEM 4.  OWNERSHIP

     (a)  Amount Beneficially Owned:
1,313,730

     (b)  Percent of Class:
5.83%

     (c)  Number of Shares as to which such person has:
1,313,730

ITEM 5.  OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS

If this statement is being filed to report the fact that as of the date hereof
the reporting person has ceased to be the beneficial owner of more than five
percent of the class of securities, check the following [___].


ITEM 6.  OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON

FRONTIER CAPITAL MANAGEMENT CO. INC. ("FRONTIER") IS AN INVESTMENT ADVISER 
REGISTERED UNDER THE INVESTMENT ADVISERS ACT OF 1940. ITS PRINCIPAL BUSINESS IS
TO PROVIDE INVESTMENT ADVISORY SERVICES TO INSTITUTIONS AND INDIVIDUALS. THE 
SHARES TO WHICH THIS STATEMENT RELATES ARE OWNED DIRECTLY BY VARIOUS ACCOUNTS
MANAGED BY FRONTIER. SUCH ACCOUNTS HAVE THE RIGHT TO RECEIVE DIVIDENDS FROM, AND
THE PROCEEDS FROM THE SALE OF, THE SHARES.

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CUSIP No.                           13G                       Page   of   Pages
896239100

ITEM 7.  IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH
ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY


ITEM 8.  IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP



ITEM 9.  NOTICE OF DISSOLUTION OF GROUP



ITEM 10.  CERTIFICATION

By signing below I certify that, to the best of my knowledge and belief, the
securities referred to above were not acquired and are not held for the purpose
of or with the effect of changing or influencing the control of the issuer of
the securities and were not acquired and are not held in connection with or as a
participant in any transaction having that purpose or effect.



DATED:                                  By: /s/ J KIRK SMITH
February 11, 2000                          Name:  J KIRK SMITH
                                           Title: EXECUTIVE VICE PRESIDENT