PSC INC.
                               PSC SCANNING, INC.
                                 675 Basket Road
                             Webster, New York 14580
                                                                   March 1, 1999

JOHN HANCOCK MUTUAL LIFE INSURANCE COMPANY
JOHN HANCOCK VARIABLE LIFE INSURANCE COMPANY
200 Clarendon Street
Boston, Massachusetts  02117

THE LINCOLN NATIONAL LIFE INSURANCE COMPANY
LINCOLN NATIONAL INCOME FUND, INC.
c/o Lincoln Investment Management, Inc.
200 East Berry Street
Renaissance Square
Ft. Wayne, Indiana  46802

SECURITY-CONNECTICUT LIFE INSURANCE COMPANY
c/o ReliaStar Investment Research, Inc.
100 Washington Avenue South
Suite 800
Minneapolis, Minnesota  55401

THE EQUITABLE LIFE ASSURANCE SOCIETY OF THE UNITED STATES
c/o Alliance Capital Management L.P.
1345 Avenue of the Americas, 37th Floor
New York, New York  10105

Re:    Amendment No. 4, Consent and Waiver Under Securities Purchase Agreements

Ladies and Gentlemen:

         PSC INC.,  a New York  corporation  (the  "Holding  Company"),  and PSC
SCANNING, INC., a Delaware corporation (formerly named SpectraScan,  Inc.) and a
Wholly-Owned  Subsidiary of the Holding Company (the  "Operating  Company") (the
Holding Company and the Operating Company are sometimes collectively referred to


<PAGE>


herein as the "Companies" and each as a "Company"), jointly and severally agree
with you as follows:

         1.  Definitions.  Reference is hereby made to those certain  Securities
Purchase  Agreements  dated July 12,  1996,  as amended  by  Amendment  No. 1 to
Securities  Purchase  Agreements  dated  October 10, 1996,  Amendment  No. 2 and
Waivers  Under  Securities  Purchase  Agreements  dated  as of July 4,  1997 and
Amendment No. 3 to Securities  Purchase Agreements and Warrants dated August 18,
1997 and as  supplemented  by the Consent and Waiver Under  Securities  Purchase
Agreements  and  Warrants  dated  December 29, 1997 (as the same may be amended,
modified  or  supplemented   from  time  to  time,  the   "Securities   Purchase
Agreements"),  among the Holding Company, the Operating Company and each of you.
Capitalized  terms used herein without  definition have the meanings ascribed to
them in the Securities Purchase Agreements.

         2. Amendment to the Securities Purchase Agreements.  Section 14.8(g) of
the  Securities  Purchase  Agreements  is hereby  amended by deleting the figure
"$3,000,000"  appearing  therein and inserting the figure  "$6,500,000" in place
thereof.

         3.       Consent and Waiver.

                  (a) Reference is hereby made to the letter dated  February 16,
         1999 from  Carey  Diversified  LLC  concerning  the  proposed  sale and
         leaseback  transaction of certain  facilities of the Operating  Company
         located in Eugene,  Oregon  (the  "Transaction"),  a true,  correct and
         complete  copy of which is  attached  hereto as  Exhibit A (the  "Carey
         Letter Agreement).

                  (b) Each of you hereby (i) consents to the consummation of the
         Transaction upon  substantially the terms set forth in the Carey Letter
         Agreement  and (ii) waives any breach of section  14.11 or 14.15 of the
         Securities  Purchase  Agreements  arising  solely on  account  thereof;
         provided that the net cash proceeds  from the  Transaction  are used to
         repay  indebtedness  outstanding  under the Bank Credit  Agreement upon
         receipt thereof.

         4.       No Default, Representations and Warranties, etc.

                  (a) The  Companies  represent  and  warrant  that,  except  as
         otherwise  modified by (i) the documents referred to in section 5(a)(i)
         of Amendment No. 3 to Securities Purchase Agreements and Warrants dated
         August 18, 1997, (ii) the projections referred to on Exhibit B attached
         to Amendment No. 2 and Waivers  under  Securities  Purchase  Agreements
         dated  as of July 4,  1997,  (iii)  the  information  delivered  to the
         Purchasers  on June 11, 1997,  which is attached to Amendment No. 2 and
         Waivers Under Securities  Purchase  Agreements dated as of July 4, 1997
         as Exhibit C, (iv) the documents referred to in Section 3(a)(iv) of

<PAGE>


         Consent and Waiver Under  Securities  Purchase  Agreements and Warrants
         dated  December 29, 1997 and (v) the following  documents  filed by the
         Holding  Company with the  Commission  under the Exchange Act: (A) Form
         10-K  for the year  ended  December  31,  1997,  (B) Form  10-Q for the
         quarters  ended April 3, 1998,  July 3, 1998 and  October 2, 1998,  (C)
         Form 10-Q/A for the quarter ended July 4, 1997, (D) Form 10-Q/A for the
         quarter  ended  October 3, 1997 and (E) Form 8-K filed on  January  15,
         1998, the  representations  and warranties  contained in the Securities
         Purchase  Agreements  and  the  other  Operative  Documents  are in all
         material  respects  correct on and as of the date  hereof as if made on
         such  date  (except  to the  extent  affected  by the  consummation  of
         transactions  permitted by the  Securities  Purchase  Agreements).  The
         Companies  further  represent and warrant that,  after giving effect to
         the provisions of this Letter Agreement, no Default or Event of Default
         exists.

                  (b) The  Companies  each  ratify and  confirm  the  Securities
         Purchase  Agreements and each of the other Operative Documents to which
         each is a party  and  agree  that each  such  agreement,  document  and
         instrument is in full force and effect, that its obligations thereunder
         and under  this  Letter  Agreement  are its  legal,  valid and  binding
         obligations enforceable against it in accordance with the terms thereof
         and  hereof and that it has no  defense,  whether  legal or  equitable,
         setoff  or   counterclaim  to  the  payment  and  performance  of  such
         obligations.

                  (c) The Companies  agree that (i) if any default shall be made
         in  the  performance  or  observance  of  any  covenant,  agreement  or
         condition  contained  in this  Letter  Agreement  or in any  agreement,
         document  or  instrument  executed in  connection  herewith or pursuant
         hereto or (ii) if any  representation or warranty made by the Companies
         herein or therein  shall prove to have been false or  incorrect  on the
         date as of which made,  the same shall  constitute  an Event of Default
         under  the  Securities  Purchase  Agreements  and the  other  Operative
         Documents  and, in such event,  you and each other holder of any of the
         Notes  shall  have all  rights  and  remedies  provided  by law  and/or
         provided or referred to in the Securities  Purchase  Agreements and the
         other Operative Documents. The Companies further agree that this Letter
         Agreement is an Operative  Document and all  references  thereto in the
         Securities  Purchase Agreements and in any other of the other Operative
         Documents shall include this Letter Agreement.

                  (d) On December 31, 1997,  each of Laserdata  Holdings,  Inc.,
         PSC S.A.,  Inc.  and PSC  Scanning  Systems,  Inc.  was merged into the
         Holding Company.

         5. Payment of Transaction Costs. The Companies shall pay all reasonable
fees  and  disbursements  incurred  by you in  connection  herewith,  including,
without  limitation,  the reasonable  fees,  expenses and  disbursements of your
special counsel.

         6. Governing Law. This Letter Agreement,  including the validity hereof
and the rights and obligations of the parties  hereunder,  shall be construed in
accordance  with and governed by the domestic  substantive  laws of the State of
New  York  without  giving  effect  to any  choice  of law or  conflicts  of law
provision or rule that would cause the  application of the domestic  substantive
laws of any other jurisdiction.
<PAGE>

         7.  Miscellaneous.  The  headings  in  this  Letter  Agreement  are for
purposes of reference  only and shall not limit or otherwise  affect the meaning
hereof.  This Letter Agreement  embodies the entire agreement and  understanding
among the parties hereto and supersedes all prior agreements and  understandings
relating to the subject  matter  hereof.  In case any  provision  in this Letter
Agreement shall be invalid, illegal or unenforceable, the validity, legality and
enforceability  of the remaining  provisions shall not in any way be affected or
impaired  thereby.  This  Letter  Agreement  may be  executed  in any  number of
counterparts  and by the parties  hereto on separate  counterparts  but all such
counterparts shall together constitute but one and the same instrument.


            [The remainder of this page is intentionally left blank.]

<PAGE>


         If you are in  agreement  with the  foregoing,  please sign the form of
agreement  on  the  accompanying   counterpart  hereof,  whereupon  this  Letter
Agreement shall become a binding  agreement under seal among the parties hereto.
Please then return one of such counterparts to the Companies.

                                Very truly yours,

                                PSC INC.



                                      By: _____________________________
                                                                (Title)


                                      PSC SCANNING, INC.



                                      By: _____________________________
                                                                (Title)


         Each of the undersigned (a)  acknowledges  and assents to the terms and
provisions of the foregoing  Letter Agreement and (b) ratifies and confirms each
of the  Operative  Documents  to which it is a party and  agrees  that each such
Operative Document is in full force and effect, that its obligations  thereunder
are  its  legal,  valid  and  binding  obligations  enforceable  against  it  in
accordance  with the terms thereof and that it has no defense,  whether legal or
equitable,  setoff or  counterclaim,  to the  payment  and  performance  of such
obligations.

                                         INSTAREAD CORPORATION


                                         By: _____________________________
                                                                 (Title)


                                         PSC AUTOMATION, INC.
                                         (formerly named Laserdata Corporation)


                                         By: _____________________________
                                                                 (Title)

<PAGE>


The foregoing is hereby accepted and agreed to:

JOHN HANCOCK MUTUAL LIFE
   INSURANCE COMPANY


By:  _____________________________
                          (Title)


JOHN HANCOCK VARIABLE LIFE
   INSURANCE COMPANY


By:  _______________________________
                          (Title)


THE LINCOLN NATIONAL LIFE
   INSURANCE COMPANY

By:    Lincoln Investment Management, Inc.
       Its Attorney-in-Fact


       By:  ___________________________
                           (Title)


LINCOLN NATIONAL INCOME FUND, INC.


By:  _______________________________
                           (Title)




<PAGE>


SECURITY-CONNECTICUT LIFE
   INSURANCE COMPANY


By:  _______________________________
                          (Title)


THE EQUITABLE LIFE ASSURANCE
   SOCIETY OF THE UNITED STATES


By:  _______________________________
                          (Title)



<PAGE>


                                    Exhibit A



                             Carey Letter Agreement


                                  See attached.