EXHIBIT 10.23



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



                                                               December 29, 1997


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 CORPORATION
SECURITY-CONNECTICUT LIFE INSURANCE COMPANY
20 Security Drive
Avon, Connecticut  06001

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:      Consent and Waiver Under Securities Purchase Agreements and Warrants

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
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 (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.
<PAGE>

         2. Consent to Rights Plan.

                  (a)  Reference  is  hereby  made to the  Summary  of Rights to
         Purchase Preferred Stock, a true, correct and complete copy of which is
         attached  hereto as Exhibit A (the  "Summary"),  the  Rights  Agreement
         referred to in the Summary,  a true, correct and complete copy of which
         is  attached  hereto as  Exhibit B (the  "Rights  Agreement"),  and the
         Certificate of Amendment  referred to in the Summary,  a true,  correct
         and  complete  copy of which  is  attached  hereto  as  Exhibit  C (the
         "Certificate of Amendment").

                  (b) Each of you hereby (i) consents to the  declaration of the
         dividend of the Rights (as defined in the Summary) in  accordance  with
         the Summary and Rights  Agreement and to the amendment of the Company's
         Organizational  Documents as provided in the  Certificate  of Amendment
         and (ii) waives any breach of section  14.6 or 14.16 of the  Securities
         Purchase  Agreements  arising solely on account thereof;  provided that
         nothing  herein  shall  be  deemed  to be (x) a  consent  to any  other
         transaction,  including,  without  limitation,  any other  issuance  of
         securities by the Holding  Company in connection with or related to the
         Rights or otherwise,  or (y) a waiver of any right of any holder of any
         Warrant  to any  adjustment  to the  Exercise  Price or the  number  of
         Warrant  Shares  issuable  upon  exercise of the Warrants  which may be
         required  under the terms of the Warrants on account of the issuance of
         the Rights or the Units  (each as defined in the  Summary) or any other
         related transaction or event.

                  (c) The  Holding  Company  agrees  that (i) the holders of the
         Warrants will be entitled to such adjustments as are provided for under
         the terms of the Warrants  upon the issuance of the Rights  and/or upon
         the  exercise  of  the  Rights,  (ii)  all  such  adjustments  will  be
         satisfactory  to the  Required  Holders  of the  Warrants  at the  time
         outstanding  and (iii) the Warrants and the Warrant Shares shall not be
         included  in  any  determination  of  whether  any  Person  or  Persons
         constitute an Acquiring Person (as defined in the Summary).


         3.   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, and (iv) the  following  documents  filed by the  Holding
         Company with the  Commission  under the Exchange Act: (A) Form 10-Q for
         the  quarters  ended July 4, 1997 and  October 3, 1997 and (B) Form 8-K
         filed  on  September  24,  1997,  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.
<PAGE>

                  (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.

         4. 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.

         5. 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.

         6.  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>


                            LASERDATA HOLDINGS, INC.



                                By: _____________________________
                                                           (Title)


                            PSC S.A., INC.



                                By: _____________________________
                                                           (Title)


                           PSC SCANNING SYSTEMS, INC.



                                By: _____________________________
                                                          (Title)



The foregoing is hereby accepted and agreed to:

JOHN HANCOCK MUTUAL LIFE
   INSURANCE COMPANY



By:  _____________________________
                                            (Title)


JOHN HANCOCK VARIABLE LIFE
   INSURANCE COMPANY



By:  _______________________________
                                            (Title)


<PAGE>


THE LINCOLN NATIONAL LIFE
   INSURANCE COMPANY

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



       By:  ___________________________
                                            (Title)


LINCOLN NATIONAL INCOME FUND, INC.



By:  _______________________________
                                            (Title)


RELIASTAR FINANCIAL CORP., as successor
   to Security-Connecticut Corporation



By:  _______________________________
                                            (Title)


SECURITY-CONNECTICUT LIFE
   INSURANCE COMPANY



By:  _______________________________
                                            (Title)


THE EQUITABLE LIFE ASSURANCE
   SOCIETY OF THE UNITED STATES



By:  _______________________________
                                            (Title)