Exhibit 10.1

                                AMENDMENT FOUR TO
                                CREDIT AGREEMENT


THIS  AMENDMENT  FOUR is dated as of April 8, 1998 and is made in respect of the
Credit  Agreement  dated  as of July  12,  1996  and as  amended  and in  effect
immediately  prior to the date hereof (the "Credit  Agreement") by and among PSC
SCANNING,  INC., a Delaware  corporation  formerly known as  SpectraScan,  Inc.,
which is the successor by merger to PSC Acquisition, Inc., (the "Borrower"), PSC
INC.  ("PSC"),  the financial  institutions  party to the Credit  Agreement (the
"Lender  Parties"),  FLEET NATIONAL BANK  (formerly  known as Fleet Bank) as the
"Initial  Issuing Bank", and FLEET NATIONAL BANK, as  administrative  agent (the
"Administrative Agent") under the Credit Agreement.

                            Statement of the Premises

The  Borrower,  PSC,  the  Lender  Parties,  the  Initial  Issuing  Bank and the
Administrative  Agent previously entered into the Credit Agreement and the First
Amendment to Credit  Agreement dated as of September 27, 1996, the Amendment Two
and Waiver to Credit  Agreement  dated as of July 4, 1997 and Amendment Three to
Credit  Agreement  (With  Consent) dated as of August 13, 1997. The Borrower has
requested  that the  Lender  Parties  amend  certain  provisions  in the  Credit
Agreement, and the Lender Parties are willing to do so.

                           Statement of Consideration

Accordingly,  in  consideration  of the  premises,  and under the  authority  of
Section 5-1103 of the New York General Obligations Law, the parties hereto agree
as follows.

                                    Agreement

1. Defined Terms. The terms "this Agreement", "hereunder" and similar references
in the  Credit  Agreement  shall be deemed to refer to the Credit  Agreement  as
amended hereby.  Capitalized  terms used and not otherwise  defined herein shall
have the meanings ascribed to such terms in the Credit Agreement.  2. Amendment.
Effective  as of April 15,  1998,  the  Credit  Agreement  is hereby  amended as
follows,  provided  that the  following  amendment  shall not be effective  with
respect to each  Eurodollar  Rate Advance made prior to April 15, 1998 until the
expiration of the current  Interest Period of each such Eurodollar Rate Advance:
2.1 Section 1.01 of the Credit  Agreement is amended by changing the definitions
of "Applicable Margin", and "Commitment Fee Percentage", as follows:

<PAGE>

     "Applicable  Margin"  means at any  time  and from  time to time a
percentage per annum determined by reference to the Total Debt Ratio as
set forth below:

                               Term A Facility and          Term A Facility
                                 Working Capital          and Working Capital
    Total Debt                      Facility              Facility Eurodollar
       Ratio                   Prime Rate Advances           Rate Advances

Level I:
a ratio greater than 3.0:1           0.500%                     2.000%

Level II:
a ratio of 3.0:1 or less
but at least 2.5:1                   0.250%                     1.750%

Level III:
a ratio of less than 2.5:1
but at least 2.0:1                   0.000%                     1.500%

Level IV:
a ratio of less than 2.0:1           0.000%                     1.250%

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                                 Term B Facility            Term B Facility
    Total Debt                                                Eurodollar
       Ratio                   Prime Rate Advances           Rate Advances

Level I:
a ratio greater than 3.0:1           1.000%                     2.500%

Level II:
a ratio of 3.0:1 or less
but at least 2.5:1                   0.750%                     2.250%

Level III:
a ratio of less than 2.5:1
but at least 2.0:1                   0.500%                     2.000%

Level IV:
a ratio of less than 2.0:1           0.250%                     1.750%

The  Applicable  Margin for each  Prime  Rate  Advance  shall be  determined  by
reference to the ratio in effect from time to time and the Applicable Margin for
each  Eurodollar  Rate Advance  shall be determined by reference to the ratio in
effect on the first day of each  Interest  Period  for such  Advance;  provided,
however,  that (A) no change in the Applicable  Margin shall be effective  until
three  Business Days after the date on which the  Administrative  Agent receives
financial statements pursuant to Section 5.03(c) or (d) and a certificate of the
chief financial officer of PSC  demonstrating  such ratio and (B) if PSC has not
submitted to the Administrative Agent the information described in clause (A) of
this proviso as and when required under Section  5.03(c) or (d), as the case may
be, the  Applicable  Margin shall be at Level I for so long as such  information
has not been received by the Administrative Agent.
<PAGE>

"Commitment Fee Percentage" means at any time and from time to time a percentage
per annum determined by reference to the Total Debt Ratio as set forth below:


Total Debt Ratio                         Commitment Fee Percentage

Level I:
a ratio of greater than 3.0:1      .                 0.500%

Level II:
a ratio of 3.0:1 or less
but at least 2.5:1                                   0.375%

Level III:
a ratio of less than 2.5:1
but at least 2.0;1                                   0.375%

Level IV:
a ratio of less than 2.0:1                           0.375%

; provided,  however,  that (A) no change in the Commitment Fee Percentage shall
be  effective   until  three   Business   Days  after  the  date  on  which  the
Administrative  Agent receives financial  statements pursuant to Section 5.03(c)
or (d) and a certificate  of the chief  financial  officer of PSC  demonstrating
such  ratio and (B) if PSC has not  submitted  to the  Administrative  Agent the
information  described in clause (A) of this proviso as and when required  under
Section 5.03(c) or (d), as the case may be, the Commitment Fee Percentage  shall
be at  Level I for so long as such  information  has not  been  received  by the
Administrative Agent.

2. Effect on the Credit  Agreement.  Except as specifically  amended above,  the
Credit  Agreement  shall remain in full force and effect and is hereby  ratified
and confirmed.  The Borrower and PSC each  acknowledge and agree that the Credit
Agreement (as amended by this  Amendment)  and each other Loan Document to which
each is a party is in full force and effect, that its Obligations thereunder and
under this Amendment are its legal,  valid and binding  obligations  enforceable
against  it in  accordance  with the terms  thereof  and  hereof,  and it has no
defense,  whether legal or equitable,  setoff or counterclaim to the payment and
performance of such Obligations.

3.  Expenses.  The  Borrower  shall pay  promptly  when  billed  all  reasonable
out-of-pocket  expenses of each of the Lender Parties and the Agent  (including,
but not limited to,  reasonable  fees,  charges and  disbursements of counsel to
each  of the  Lender  Parties  and  the  Agent)  incident  to  the  preparation,
negotiation,  execution,  administration  and  enforcement of the this Amendment
Four and all  documents  and  transactions  required  in  connection  with  this
Amendment Four.

4.  Execution in  Counterparts  and  Effectiveness.  This  Amendment Four may be
executed in any number of  counterparts  and by the different  parties hereto on
separate counterparts,  each of which shall be deemed to be an original, and all
of which  taken  together  shall  constitute  one and the same  Amendment  Four,
regardless  of whether or not the  execution by all parties  shall appear on any
single counterpart.  Delivery of an executed  counterpart of a signature page to
this Amendment  Four by telecopier  shall be effective as delivery of a manually
executed  counterpart  of  this  Agreement.  This  Amendment  Four  will  become
effective  (subject  to the terms of  Section 2 above)  when the  Administrative
Agent shall have received  counterparts of this Amendment Four which, when taken
together, bear the signatures of the Borrower, PSC, the Administrative Agent and
all of the Lenders.

5.  Applicable  Law.  Pursuant  to  Section  5-1401  of  the  New  York  General
Obligations  Law, the laws of the State of New York shall  govern the  validity,
construction,  enforcement  and  interpretation  of this Amendment Four in whole
without  regard  to any  rules  of  conflicts-of-laws  that  would  require  the
application of the laws of any jurisdiction other than the State of New York.

6.  Headings.  The  headings  of this  Amendment  Four are for the  purposes  of
reference only and shall not limit or otherwise affect the meanings  hereof.  IN
WITNESS WHEREOF,  the parties hereto have caused a counterpart of this Amendment
Four to be executed and delivered by their respective  representatives thereunto
duly authorized, as of the date first above written.

<PAGE>


PSC INC.                                   PSC SCANNING, INC.

By:                                        By:
Title:   Vice President, Chief Financial   Title:   Vice President and Chief
         Officer & Treasurer               Financial Officer


FLEET NATIONAL BANK, as Initial             FLEET NATIONAL BANK, as
Issuing Bank                                Administrative Agent

By:                                         By:
Title:                                      Title:


FLEET NATIONAL BANK                         CORESTATES BANK, N.A.

By:                                         By:
Title:                                      Title:


MANUFACTURERS & TRADERS                     KEY BANK NATIONAL
TRUST COMPANY                               ASSOCIATION

By:                                         By:
Title:                                      Title:


                                            PILGRIM AMERICA PRIME RATE
THE SUMITOMO BANK, LIMITED                  TRUST

By:                                         By:
Title:                                      Title: