
<PAGE>

                                                                       Exhibit A

                                                                  [LOGO] HEWLETT
                                                                         PACKARD

October 21, 1999

Mr. David T. Giddings
Diametrics Medical, Inc.
2658 Patton Road
St. Paul, MN 55113-1136

Re: Realignment of Hewlett-Packard Company

Dear Mr. Giddings:

Hewlett-Packard Company ("HP") wishes to notify you that it plans for a
strategic realignment of its businesses to create two independent companies (the
"Realignment"). The Realignment will be accomplished by operating HP's
measurement businesses as a new company ("Agilent Technologies") to be owned by
stockholders of the Company and, potentially, by other investors. Agilent
Technologies will be comprised of HP's Test and Measurement Organization,
Medical Products Group, Semiconductor Products Group, and Chemical Analysis
Group, which had combined revenues of approximately $8 billion in 1998. Agilent
Technologies will continue to design, manufacture and sell computers, equipment,
systems and services for use in a variety of applications.

The Common Stock Purchase Agreement entered into by Diametrics Medical, Inc. and
HP dated June 6, 1999 (the "Agreement") will remain with Agilent Technologies,
which looks forward to continuing to conduct business with you under the
Agreement. We ask that you indicate your receipt of this letter by signing in
the space indicated below and returning it to me by fax at (978) 683-5323 no
later than October 15, 1999, and returning your original signed letter in the
enclosed envelope at your earliest convenience. Your signature below will also
constitute a waiver of any notice period that may be required by the Agreement.

Please call me at (978) 659-4729 if you have any questions concerning this
letter or the Realignment. Thank you for your cooperation in this matter.

Very truly yours,

HEWLETT-PACKARD COMPANY


By: /s/ Reed Malleck
   --------------------------------
    Reed Malleck
Controller, Patient Monitoring Division

cc:  Dorsey and Whitney
     Attn:  Kenneth L. Cutler
     220 S. 6th Street
     Minneapolis, MN 55402-1498
Enclosure
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UNDERSTOOD AND AGREED:

By: /s/ David T. Giddings
   ----------------------

Title:  CEO
      -------------------

Date:   10/30/99
     --------------------


