EXHIBIT 4.3     
                                                                  
                                                               May 11, 1995     
   
Mr. John J. Van Buren     
Senior Vice-President and CFO     
Datametrics Corporation     
21135 Erwin Street     
Woodland Hills, CA 91367     
   
Dear Jack,     
   
  Reference is made to that certain Letter Agreement dated February 17, 1995 by
and between Datametrics Corporation and Cruttenden Roth Incorporated (the
"Letter Agreement"). Through this amendment letter, Datametrics and Cruttenden
Roth hereby agree that the Letter Agreement shall be amended as follows:     
     
    1. The parties agree that Cruttenden Roth will not receive 170,000 new
  five-year warrants pursuant to the Letter Agreement. Accordingly, the
  second (2nd) paragraph under Section 1 of the Letter Agreement, commencing
  with the phrase, "Also on the Closing Date," shall be deleted in its
  entirety.     
     
    2. The sixth (6th) and eight (8th) sentences of the first (1st) paragraph
  under Section 1 of the Letter Agreement are deleted in their entirety and
  the same are replaced by the following: "The parties agree that Datametrics
  shall use reasonable efforts to cause its Registration Statement on Form S-
  3 filed April 11, 1995 to be declared effective as promptly as practicable
  following the date hereof. Cruttenden Roth shall exercise its warrants on
  the effective date of such registration statement."     
     
    3. The parties agree that the provisions of Section 2 of the Letter
  Agreement have lapsed and that neither party has any obligation to the
  other thereunder.     
   
  If this amendment to the Letter Agreement meets with your approval please
indicate your acceptance and agreement by executing this letter amendment and
returning a copy to us.     
                                          
Sincerely,                                Agreed by,     
CRUTTENDEN ROTH                           DATAMETRICS CORPORATION     
INCORPORATED     
                                          
Michael Walthall                          John J. Van Buren     
Vice-President                            Senior Chief Vice-President     
                                          and Chief Financial