Two books are listed in the books section that would be of interest to me, but the contact email for the first bounces.
A Guide To HP Handheld Calculators and Computers
W. A. C. Mier-Jedrzejowicz, Ph.D., Wilson/Barnett Publishing, Tustin CA, 1996.
ISBN 1-888840-00-5
Customize your HP-28
W. A. C. Mier-Jedrzejowicz, Ph.D.
Is there a new email address or contact info?
thanks-
Christof