EXHIBIT 10.26

December 18, 1998



Mr. Larry Gerhard
Summit Design, Inc.
9305 S.W. Gemini Drive
Beaverton, OR  97008

RE:  Software OEM License Agreement between Summit Design, Inc. (SDI) and 
Credence Systems Corporation (CSC) dated July 11, 1997 ("OEM Agreement")

Dear Larry:

The OEM agreement provides for a maximum shipment of VTB licenses by SDI in 
each quarter.  CSC hereby requests the following change in the Schedule D 
License Fee and Payment:



     Quarterly Maximum Shipments
                                     Current   Requested
                                     -------   ---------
                                         
     Q4 1998   Licenses at *            *          *

     Q1 1999   Licenses at *            *          *
     Q2 1999   Licenses at *            *          *
     Q3 1999   Licenses at *            *          *
     Q4 1999   Licenses at *            *          *
                                       ---        ---
                  Total                 *          *
                                       ---        ---


CSC will authorize payment one day after shipment of licenses provided that 
SDI agrees that the OEM Agreement is thereby terminated with no restrictions 
on any subsequent use, sale, license or distribution of the VTB Software 
purchased by CSC under the OEM Agreement.

Sincerely,

/s/ Jerry Bruce

Jerry Bruce
Vice President, Treasurer and Corporate Controller
Credence Systems Corporation

Agreed:


/s/ Larry J. Gerhard
- -------------------------------------
Larry J. Gerhard



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  the Commission.  Confidential treatment has been requested with respect to 
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