Hewlett Packard HP-28S/C

HP-28C Serial Number (1) 2710A00461: 1987, 10th week, America
Accessories Manual: HP-28C Benutzerhandbuch (Einführung), Nov 1986 (German)

Manual: HP-28C Referenzhandbuch, Oct 1986 (German)

Software: "Version 1BB"
Condition Excellent! On the back side a small piece of the lower left rubber foot is missing
Acquired 23.10.2002
HP-28S Serial Number (2) 2826A00405: 1988, 26th week, America
Accessories Manual: HP-28C/S Advanced Scientific Calculator Referenzhandbuch, Feb 1988 (German)
Note that this Reference Manual does not cover the special features of the HP-28S!

Software: "Version 2BB Copyright HP 1986, 1987"
Condition Very good. There is a small piece of plastic broken off next to the battery compartment
Acquired 26.10.2002


HP-28S Serial Number (3) 3146S01332: 1991, 46th week, Singapore
Accessories Manual: HP-28S Advanced Scientific Calculator Benutzerhandbuch (Geman), Sep 1988

Manual: HP-28C/S Advanced Scientific Calculator  Referenzhandbuch (Geman), Sep 1988

Software: "Version 2BB Copyright HP 1986, 1987"
Condition Mint!!
Acquired 15.1.2003

HP-28S Serial Number (4) 2922A34048: 1989, 22nd week, America
Accessories None

Software: "Version 2BB Copyright HP 1986, 1987"
Condition Mint!
Acquired 23.11.2003
HP-28C in der Praxis
Book Hewlett-Packard HP-28C/HP-28S im Einsatz, Rainer Stahl (German), Vieweg Verlag, ISDN 3-528-14648-6, 226 pages
Solutions of Equations, Investigation of Functions, Matrix Calculation
Interpolation, Approximation, Differential Equations, Eigenvalues
Condition Almost mint!
Acquired 17.5.2003

Book Mathematische Anwendungen, Schrittweise Lösungen für Ihren Taschenrechner HP-28S (German, 2nd extended edition, April 1990, 120 pages)
Polynomials, differential equations, coordinate transformations, curve fitting, triangular calculations, miscellaneous
Condition Excellent!
Acquired 12.2.2004

Book Step-by-Step Solutions For Your HP Calculator: Algebra and College Math

English, 1st edition, 1.12.1987, 125 pages
Functions and Equations, Infinite Sequences and Series, Determinants of Matrices, Logarithms, Trigonometry, Geometry.
Condition Average.
Acquired 22.2.2004

Book Hewlett packard Step-by-Step Solutions For Your HP Calculator: Calculus (English), 2.6.1988, 95 pages
Function Operations, Differential Calculus, Integral Calculus
Comment Bound printout from MoHPC CD-ROMs
Hewlett packard Step-by-Step Solutions For Your HP Calculator: Probability and Statistics (English), 1.11.1987, 77 pages
Statistics Matrix Setup, Basic Statistics for Multiple Variables, Regression, Test Statistics and Confidence Intervals, Combinations and Permutations
Bound printout from MoHPC CD-ROMs
Hewlett packard Step-by-Step Solutions For Your HP Calculator: Vectors and Matrices (English), 3.6.1989, 108 pages
General Matrix Operations, Systems of Linear Equations, Vector Spaces, Eigenvalues, Least Squares, Markov Chains, A Sample Appliaction
Bound printout from MoHPC CD-ROMs

HP codename, series Paladin (HP-28C), Orlando (HP-28S), Champion/Clamshell
Type, Precision, Input Mode Scientific, 12 BCD digits, exponent ±499, Reverse Polish Notation
Programmable Yes, in RPL (Reverse Polish Lisp) with arbitrary program and variable names. In fact, a program is treated as a variable containing program code (other variable types are strings, numbers, vectors, matrices, lists).
It turns out that the HP-28S is a surprisingly fast unit! It easily beats the Casio fx-880P, Casio fx-2000C, TI-74 and the HP-32SII. Compared to the HP-15C/41CV/CX it is about 20 times as fast. Only the HP-48GX/HP-49G are significantly faster.
The RPL programming model is similar to the HP-48GX and HP-49G. 
Performance Index HP-28S: 54
Memory HP-28C: 2048 bytes, HP-28S: 32kByte
All variables, programs and the (infinite) stack are stored in this permanent memory.
Display 138x32 pixel black&white LCD, 23x4 characters
Special features Folding design, the top half can be flipped all the way to the back of the calculator, 72 (!) keys.
User/system RPL (Reverse Polish Lisp) programming language.
Many data types: Real numbers, complex numbers, real & complex vectors, real & complex matrices, lists, integer numbers up to 64 bits, strings.
Symbolic equation manipulation (ie. differentiation, integration), structured programming, graphics. A wealth of built-in unit conversions. Numerical root finding (solver) and integration. Directory-oriented file system, online help catalog of built-in functions and unit conversions. Infrared printer port, works with the HP Infrared Printer.
Original Pricing, Production HP-28C: 5.1.1987 ($235) - 1/1988 ($235)
HP-28S: 4.1.1988 ($235) - 1.4.1992 ($195)
Batteries 3xN
Dimensions Length 15.9cm, Width 9.4cm (closed), 18.9cm (open) Height 1.8cm (closed)
Links HP-28C Reference Manual, Jan 1987 (PDF)
HP-28C Getting Started Manual, Jan 1987 (PDF)
HP-28S Owner's Manual, Nov 1988 (PDF)
HP-28S Reference Manual, Nov 1988 (PDF)
A number of interesting programs (PDF)
HP-28S Software Power Tools (PDF)
Quick Reference (PDF)
Step-by-Step Solutions For Your HP Calculator, Calculus, HP-28S, HP-28C (English) 2.6.1988
Step-by-Step Solutions For Your HP Calculator, Probability and Statistics, HP-28S, HP-28C (English) 1.11.1987
Step-by-Step Solutions For Your HP Calculator, Vectors and Matrices, HP-28S, HP-28C (English) 3.6.1989
HP-28C Hardware I/O Basics (MoHPC)
Utility Programs.
HP-28COM Serial Interface.
Infrared Interface Format.
Power Consumption.
Available Accessories.
Comments The HP-28C was Hewlett Packard's first unit using the RPL programming language.
What a device! The designes really put a lot of thought in this powerful unit, see special features above. Despite all this power and the vast number of functions is the HP-28 fairly easy to use - at least after spending a small initial effort needed to understand the basic concepts.
There's really not much missing except maybe that its response on inputs feels a bit sluggish. Also - more importantly - its programming model is missing the C-style BREAK instruction needed for early termination of FOR-NEXT, DO-UNTIL and WHILE-REPEAT loops. And although it had an infrared printer port it lacked the HP-41C's famous I/O capabilties.
Nevertheless, it was HP's only true pocket-sized calculator that offered the powerful RPL language. All other RPL models (HP-48/49/50) were quite big. Only the HP-41C and HP-42S offered a sufficiently powerful keytroke-based programming model with arbitrary program names that allowed to build entire program libraries. HP's later pocket-sized models (HP-32S/II, HP-33S, HP-35S) had a rather restricted "A...Z" program naming scheme.
  • The HP-28C came with two different software versions: 1BB and 1CC (late 1987).
  • Select Hex mode and enter "#A SYSEVAL" to retrieve the software version number on the HP-28C and HP-28S.
Software Bugs Version 1BB bugs (thanks to C. Finseth):
  • Turn a unit on and keep the ON key pressed for a moment. Now press SHIFT. There is a 50% chance that the unit will turn off.
  • Using the Solver with a program that does not return an object to the stack. Sometimes a system object will be placed there.
  • Trying to delete an empty row with shift INS while editing a command line can lead to strange results and possibly a Memory Lost.
  • Dividing a 64 bit number with its top bit set can give wrong answers.
  • Otherwise equal binary integers with different word sizes do not necessarily compare equal. Try: #1 DUP 50 STWS 'A' STO 'A ENTER ==
  • If flags 57 or 58 are set the Solver might give an underflow or overflow error while working to a solution.
  • The Solver can also give incorrect Sign Reversal messages.
  • User-defined units that are multiples of degrees Farenheight or Celsius give incorrect results.
  • The unit "yr" has been defined as 365 days instead of the correct 365.242 days.  As "lyr" is defined in terms of this unit, it, too is incorrect.
  • RND does not work correctly in FIX mode (try "0 FIX .7 RND": you get 0 instead of 1, unless you have flag 51 or 52 set!).  If you don't want to set one of these flags, use ->STR STR-> to round the number.
  • Actually, this demonstrates another problem.  Do: "0 FIX MAXR ->NUM" and you get 1.E500.  Now, ->STR gives "1.E500" then STR-> gives Syntax Error.
  • String comparisons produce incorrect results if the strings do not differ in their initial letter: "AA" "AB" < gives 0.
  • EDIT and VISIT can give unexpected results if you attempt to EEX or CHS an already-existing number.  Use "-" and "E" or delete and reenter the number.
  • Memory can be corrupted by incorrect usages of the derivative function.
  • Merging left with the divide sign can give incorrect results.
  • Rounding of numbers in complex and matrix operations is sometimes slightly different than that of the same pure real numbers.
  • When the origin is not on the screen, plot tick marks are relative to the screen instead of the origin.
  • The Out of Memory condition does not clear typeahead: you may unexpectedly delete variables or programs.
  • The Solver does not always clear all internal flags.  Do:
Memory Lost
0 1/X       (gives "Infinite result" and sets flag)
<< A DROP 1 >> STEQ

Solve for A without an initial guess.  You will get a System Halt.
  • Non-real results can cause the Solver to store a system object as the variable's value.
  • Some special characters are not displayed on the menu line properly:
character           displays as
&                   e
|                   Z
~                   \
\.x                 `
\:-                 _
proportionality     o]
(140 decimal)

  • (Not really a bug) Turning a string into a name, where the string refers to a name that already exists, will always hang due to inifinite evaluation recursion.
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