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The HP-42S
Type Programmable scientific
Manufacturer Hewlett Packard
Introduced 1988
Discontinued 1995
Entry mode RPN
Precision 12 display digits (15 digits internally),[1] exponent ±499
Display type LCD Dot-matrix
Display size 2 lines, 22 characters, 131x16 pixels
Processor Saturn
Programming language(s) RPN key stroke (fully merged, Turing complete)
Firmware memory 64 KB of ROM
Program steps 7200
Ports IR (Infrared) printing
Power supply 3×1.5V button cell batteries (Panasonic LR44, Duracell PX76A/675A or Energizer 357/303)
Weight 6 oz (170 g)
Dimensions 148×80×15mm

The HP-42S is a programmable RPN Scientific hand held calculator introduced by Hewlett Packard in 1988. It has advanced functions suitable for applications in mathematics, linear algebra, statistical analysis, computer science and others.

HP-41 replacement[edit]

Perhaps the HP-42S was to be released as a replacement for the aging HP-41 series as it is designed to be compatible with all programs written for the HP-41. Since it lacked expandability, and lacked any real I/O ability, both key features of the HP-41 series, it was marketed as an HP-15c replacement.

The 42S, however, has a much smaller form factor than the 41, and features many more built-in functions, such as a matrix editor, complex number support, an equation solver, user-defined menus, and basic graphing capabilities. Additionally, it features a two-line dot matrix display, which made stack manipulation easier to understand.

Production of the 42S ended in 1995.[citation needed] In the HP calculator community, the 42S is infamous for its high prices in online auctions, the rare new-in-box calculators typically command in excess of $400 USD.[citation needed] This is nearly a four-fold increase in price over its introduction cost and has created a scarcity for utility end users. Yet, this calculator is often regarded as the best ever made in terms of quality, key stroke feel, ease of programming, and daily usability for engineers. Many scientists and engineers use this calculator today, 25 years after its introduction.[citation needed]

HP-42S specifications[edit]

HP-42S battery compartment and the IR diode
  • Series: Pioneer
  • Code Name: Davinci
  • Introduction: 1988-10-31
  • 64 KB of ROM
  • 8 KB of RAM
  • Functions: Over 600
  • Expandability: Officially no other than IR printing (32K memory upgrade and over-clocking hardware hacks are possible)
  • Peripherals: HP-82240B Infrared Printer

HP-42S features[edit]


Main article: Focal (HP-41)

The HP-42S is keystroke-programmable, meaning that it can remember and later execute sequences of keystrokes to solve particular problems of interest to the user. The HP-42S uses a superset of the HP-41CX FOCAL language (unrelated to the DEC FOCAL programming language).

The HP-42S supports indirect addressing with which it is possible to implement a Universal Turing machine and therefore the programming model of the HP-42S can be considered Turing-complete.

Sample program[edit]

This is a sample program which computes the factorial of an input integer number (ignoring the calculator's built-in factorial function). The program consumes 18 bytes. No memory registers are used.

Step Instruction Comment
01 LBLFAC Start of program "FAC"
02 1 1 is put into X, hence the value to be calculated upon (which was initially in X) is lifted (pushed) into stack register Y
03 LBL00 Define label 00
04 RCL×STY Recall stack register Y and multiply with X
05 DSESTY Decrement stack register Y and if not zero ...
06 GTO00 ... go back to label 00
07 END or RTN Returns control (and result in X) to either the user or to a calling program.


  1. ^ HP-42s Owner's Manual. Corvallis, OR: Hewlett-Packard Co. 1988. p. 3. 

External links[edit]