EXHIBIT 4.1
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                AMENDMENT NO. 1 TO SHAREHOLDER RIGHTS AGREEMENT
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          This amendment, dated as of December 20, 1997, amends the Shareholder
Rights Agreement dated as of February 16, 1989, as amended and restated as of
March 12, 1990 (the "Rights Agreement") between Dynatech Corporation (the
"Company") and BankBoston, N.A. (formerly The First National Bank of Boston), as
Rights Agent (the "Rights Agent").  Terms defined in the Rights Agreement and
not otherwise defined herein are used herein as so defined.

                              W I T N E S S E T H
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          WHEREAS, on February 16, 1989 the Board of Directors of the Company
authorized the issuance of Rights to purchase, on the terms and subject to the
provisions of the Rights Agreement, one share of the Company's Common Stock, par
value $.20 per share; and

          WHEREAS, on February 16, 1989, the Board of Directors of the Company
authorized and declared a dividend distribution of one Right for every share of
Common Stock of the Company outstanding on the Record Date and authorized the
issuance of one Right (subject to certain adjustments) for each share of Common
Stock of the Company issued between the Record Date and the Distribution Date;
and

          WHEREAS, on February 16, 1989, the Company and the Rights Agent
entered into the Rights Agreement, which was amended and restated on March 12,
1990 to set forth the description and terms of the Rights; and
 
          WHEREAS, pursuant to Sections 27 and 29 of the Rights Agreement, the
Company now desires to amend certain provisions of the Rights Agreement in order
to supplement certain provisions therein;

          NOW, THEREFORE, the Rights Agreement is hereby amended as follows:

          1.   Section 1(a) is amended by adding the following at the end
               thereof:

               "; and, provided, further, that as a result of the execution,
               delivery and performance under, or consummation of the
               transactions relating to and contemplated by the Agreement and
               Plan of Merger dated as of December 20, 1997 by and among the
               Company and CDRD Merger Corporation (the "Merger Agreement") CDRD
               Merger Corporation shall not be deemed an Acquiring Person for
               any purpose of this Agreement."

          2.   Section 1(b) is amended by adding the following at the end
               thereof:

               "provided, however, that CDRD Merger Corporation shall not,
               during the effectiveness of the Merger Agreement, be declared an
               Adverse Person for any purpose of this Agreement."

 
          3.   Section 7(a) is amended to read in its entirety as follows:

               " (a) Subject to Section 7(e) hereof, the registered holder of
               any Right Certificate may exercise the Rights evidenced thereby
               (except as otherwise provided herein) in whole or in part at any
               time after the Distribution Date upon surrender of the Right
               Certificate, with the form of election to purchase and the
               certificate on the reverse side thereof duly executed, to the
               Rights Agent at the office or offices of the Rights Agent
               designated for such purpose, together with payment of the
               aggregate Exercise Price for the total number of one two-
               thousandths of a share of Preferred Stock (or other securities,
               cash or other assets, as the case may be)  as to which such
               surrender Rights are then exercised, at or prior to the earlier
               of (i) the earlier of the Effective Time (as defined in the
               Merger Agreement) and the close of business on February 16, 1999
               (the "Final Expiration Date") or (ii) the time at which the
               Rights are redeemed as provided in Section 23 hereof (the earlier
               of (i) or (ii) being herein referred to as the "Expiration
               Date"). Except as set forth in Section 7(e) hereof and
               notwithstanding any other provision of this Agreement, any Person
               who prior to the Distribution Date becomes a record holder of
               shares of Common Stock may exercise all of the rights of a
               registered holder of a Right Certificate with respect to the
               Rights associated with such shares of Common Stock in accordance
               with the provisions of this Agreement, as of the date such Person
               becomes a record holder of shares of Common Stock.

          4.   Except as expressly herein set forth, the remaining provisions of
               the Rights Agreement shall remain in full force and effect.

          IN WITNESS WHEREOF, this Amendment No. 1 has been signed to be
effective as of the close of business on the 20th day of December, 1997 by
authorized representatives of each of the Company and the Rights Agent.

                                       DYNATECH CORPORATION



                                       By: /s/ Allan M. Kline
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                                       BANKBOSTON, N.A.



                                       By:  /s/ Carol Mulny-Eori
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