KEI Keithley Instruments, Inc.

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

SCHEDULE 13G/A

UNDER THE SECURITIES EXCHANGE ACT OF 1934
(AMENDMENT NO. 4)*

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 the disclosures provided in a prior cover page.

The information required in 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).

PAGE 1 OF 4 PAGES

 NWQ Investment Management Company, LLC 47-0875103
--------------------------------------------------------------------------------
 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) [_]
 (b) [_]
--------------------------------------------------------------------------------
 3 SEC USE ONLY

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

 Delaware - U.S.A.
--------------------------------------------------------------------------------
 5 SOLE VOTING POWER

 478,144
 NUMBER OF -----------------------------------------------------------
 SHARES 6 SHARED VOTING POWER
 BENEFICIALLY
 OWNED BY 0
 EACH -----------------------------------------------------------
 REPORTING 7 SOLE DISPOSITIVE POWER
 PERSON
 WITH 619,784
 -----------------------------------------------------------
 8 SHARED DISPOSITIVE POWER

 0
--------------------------------------------------------------------------------

9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

PAGE 2 OF 4 PAGES

Item 1(a) Name of Issuer:
Keithley Instruments Inc.

Item 1(b) Address of Issuer's Principal Executive Offices:
28775 Aurora Road Cleveland, Ohio 44139-1891 United States

Item 2(a) Name of Person Filing:
NWQ Investment Management Company, LLC

Item 2(b) Address of the Principal Office or, if none, Residence:
2049 Century Park East, 16th Floor Los Angeles, CA 90067

Item 2(c) Citizenship:
Delaware - U.S.A.

Item 2(d) Title of Class of Securities:
Common

Item 2(e) CUSIP Number:
487584104

Item 3 If the Statement is being filed pursuant to Rule
13d-1(b), or 13d-2(b), check whether the person filing is a:

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

Item 4 Ownership:
(a) Amount Beneficially Owned:

619,784

(b) Percent of Class:

4.55%

(c) Number of shares as to which such person has:
(i) sole power to vote or direct the vote:

478,144

(ii) shared power to vote or direct the vote:

0

(iii) sole power to dispose or to direct the disposition of:

619,784

(iv) shared power to dispose or to direct the disposition of:

0

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. {X}

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Item 6 Ownership of More than Five Percent on Behalf of Another Person:

Securities reported on this Schedule 13G are beneficially owned by clients of the adviser, which may include investment companies registered under the Investment Company Act and/or employee benefit plans, pensions, Charitable funds or other institutional and high net worth clients.

Item 7 Identification and Classification of the Subsidiary Which Acquired
the Security Being Reported on By the Parent Holding Company:
Not applicable.

Item 8 Identification and Classification of Members of the Group:
Not applicable.

Item 9 Notice of Dissolution of a Group:
Not applicable.

Item 10 Certification:
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and 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 such securities and were not acquired in connection with or as a participant in any transaction having such purpose or effect.

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: August 9, 2010

NWQ Investment Management Company, LLC

By: /s/ Jon D. Bosse
 -------------------------------
 Jon D. Bosse, CFA
 Title: Chief Investment Officer

PAGE 4 OF 4 PAGES

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