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Exhibit 31(b)

Certification Pursuant to Rule 13a-14(a)/15d-14(a)

I, Mark J. Plush, certify that:



| | 1. |  | I have reviewed this quarterly report on Form 10-Q of Keithley
Instruments, Inc.;                                                                                                                                                                                                                         
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|
| | 2. |  | Based on my knowledge, this report does not contain any untrue
statement of a material fact or omit to state a material fact necessary
to make the statements made, in light of the circumstances under which
such statements were made, not misleading with respect to the period
covered by this report;
|
| | 3. |  | Based on my knowledge, the financial statements, and other
financial information included in this report, fairly present in all
material respects the financial condition, results of operations and
cash flows of the registrant as of, and for, the periods presented in
this report;                   
|
| | 4. |  | The registrants other certifying officers and I are responsible
for establishing and maintaining disclosure controls and procedures (as
defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the
registrant and have:                                                                              



| | a) |  | designed such disclosure controls and procedures, or
caused such disclosure controls and procedures to be designed
under our supervision, to ensure that material information
relating to the registrant, including its consolidated
subsidiaries, is made known to us by others within those
entities, particularly during the period in which this report is
being prepared;         
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|
| | b) |  | evaluated the effectiveness of the registrants
disclosure controls and procedures and presented in this report
our conclusions about the effectiveness of the disclosure
controls and procedures, as of the end of the period covered by
this report based on such evaluation; and                                                                                                    
|
| | c) |  | disclosed in this report any change in the registrants
internal control over financial reporting that occurred during
the registrants most recent fiscal quarter (the registrants
fourth fiscal quarter in the case of an annual report) that has
materially affected, or is reasonably likely to materially
affect, the registrants internal control over financial
reporting; and



| | 5. |  | The registrants other certifying officers and I have disclosed,
based on our most recent evaluation of internal control over financial
reporting, to the registrants auditors and the audit committee of the
registrants board of directors (or persons performing the equivalent
functions):
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| | a) |  | all significant deficiencies and material weaknesses in
the design or operation of internal control over financial
reporting which are reasonably likely to adversely affect the
registrants ability to record, process, summarize, and report
financial information; and
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|
| | b) |  | any fraud, whether or not material, that involves
management or other employees who have a significant role in the
registrants internal control over financial reporting.                                                                                                

|                      |  |                                                             
|--------------------- |  | ------------------------------------------------------------
|Date: August 13, 2003 |  | /s/ Mark J. Plush
Vice President and Chief Financial Officer