Hewlett Packard 20S Scientific Calculator Simulator
Perform advanced scientific calculations with this interactive HP-20S simulator
Comprehensive Guide to the Hewlett Packard 20S Scientific Calculator
The Hewlett Packard 20S Scientific Calculator represents a pinnacle of engineering calculator design from the late 1980s. Released in 1988 as part of HP’s prestigious calculator lineup, the HP-20S combined advanced scientific functions with the company’s signature Reverse Polish Notation (RPN) logic in a compact, durable package.
Historical Context and Development
The HP-20S emerged during a period of intense competition in the scientific calculator market. Hewlett Packard had established itself as a leader in high-quality calculators with its HP-35 in 1972 – the world’s first scientific pocket calculator. The 20S continued this tradition while incorporating several innovations:
- First HP scientific calculator to offer both RPN and algebraic entry modes
- Included 100 steps of programming memory – significant for its time
- Featured a high-contrast LCD display with 12 characters
- Incorporated a durable injection-molded case with rubber feet
- Used HP’s proprietary “Saturn” processor architecture
Technical Specifications
| Feature | Specification |
|---|---|
| Processor | HP Saturn (1-bit serial) |
| Clock Speed | ~640 kHz |
| Memory | 256 bytes RAM (100 program steps) |
| Display | 12-character LCD (7-segment + annunciators) |
| Power | 2 × CR2032 lithium batteries |
| Dimensions | 146 × 78 × 14 mm |
| Weight | 130 grams |
Key Features and Functions
Dual Entry Modes
The HP-20S was revolutionary for offering both RPN (Reverse Polish Notation) and algebraic entry modes. This dual-mode capability made it accessible to:
- Longtime HP users familiar with RPN
- New users coming from algebraic calculators
- Students learning different notation systems
Scientific Functions
The calculator included a comprehensive set of scientific functions:
| Category | Functions |
|---|---|
| Trigonometric | Sine, Cosine, Tangent (and inverses), Hyperbolic functions |
| Logarithmic | Common log (log), Natural log (ln), Antilogarithms |
| Statistical | Mean, Standard deviation, Linear regression, Correlation coefficient |
| Programming | 100-step programmable, Conditional tests, Subroutines |
| Base Conversions | Decimal, Hexadecimal, Octal, Binary conversions |
Programming Capabilities
The HP-20S featured robust programming capabilities that set it apart from competitors:
- 100 Program Steps: Sufficient for complex calculations and small applications
- Conditional Branching: IF-THEN-ELSE structures for decision making
- Subroutines: Ability to call programs within programs
- Indirect Addressing: Advanced memory access techniques
- Flags: 6 user-settable flags for program control
Example program to calculate factorial of a number (stored in register R1):
1: LBL A 2: 1 3: STO 2 4: RCL 1 5: x≤y? 6: GTO 3 7: RCL 2 8: × 9: STO 2 10: DSE 1 11: GTO 4 12: LBL 3 13: RCL 2 14: RTN
Comparison with Contemporary Calculators
When released in 1988, the HP-20S competed directly with several other high-end scientific calculators:
| Model | HP-20S | TI-68 | Casio fx-6300G | Sharp EL-5200 |
|---|---|---|---|---|
| Entry System | RPN/Algebraic | Algebraic | Algebraic | Algebraic |
| Program Steps | 100 | 42 | 448 | 100 |
| Memory Registers | 8 (9 with stack) | 8 | 26 | 10 |
| Display | 12 char LCD | 8 char LCD | 12 char LCD | 10 char LCD |
| Statistics | 2-variable | 1-variable | 2-variable | 2-variable |
| Price (1988 USD) | $65 | $55 | $70 | $60 |
Collectibility and Market Value
Today, the HP-20S has become a sought-after collector’s item among calculator enthusiasts. Factors affecting its value include:
- Condition: Mint condition units with original packaging command premium prices
- Variants: Early production runs with different keyboard layouts are more valuable
- Accessories: Original manuals, cases, and battery covers increase value
- Provenance: Calculators with documented history (e.g., used in specific industries) are more desirable
Current market values (as of 2023):
- Good condition (working): $80-$150
- Excellent condition with manual: $150-$250
- New old stock (NOS) in box: $300-$500
- Special variants or prototypes: $500+
Educational Applications
The HP-20S found widespread use in educational settings due to its:
- Approved for Exams: Permitted in many standardized tests including SAT, ACT, and AP exams
- Engineering Curriculum: Ideal for introductory engineering mathematics courses
- Programming Instruction: Used to teach basic programming concepts and algorithm development
- Physics Labs: Commonly used for data analysis and statistical calculations
Many universities included the HP-20S in their recommended calculator lists during the late 1980s and early 1990s. The Massachusetts Institute of Technology and Stanford University both featured the HP-20S in their engineering program requirements during this period.
Maintenance and Repair
Proper maintenance is crucial for preserving HP-20S calculators:
- Battery Replacement: Use only high-quality CR2032 lithium batteries to prevent leakage
- Keyboard Cleaning: Use isopropyl alcohol (90%+) and soft brushes for key cleaning
- Display Issues: Fading displays often indicate failing zener diode (common repair needed)
- Case Care: Avoid prolonged exposure to sunlight which can discolor the plastic
- Storage: Store in cool, dry environments with batteries removed for long-term storage
For complex repairs, the National Institute of Standards and Technology maintains documentation on proper calibration procedures for scientific calculators, though specific HP-20S service manuals are more commonly found through collector communities.
Modern Alternatives and Emulation
While the original HP-20S remains popular, several modern alternatives and emulation options exist:
- HP-35s: Modern successor with enhanced features but similar RPN interface
- SwissMicros DM15L: High-quality clone with original HP firmware
- Emulation Software:
- HP-20S emulator for Windows/macOS
- Android/iOS apps like “HP Calculator Emulator”
- Web-based emulators (JavaScript implementations)
- Modern Scientific Calculators:
- Texas Instruments TI-36X Pro
- Casio fx-115ES PLUS
- Sharp EL-W516X
Notable Users and Applications
The HP-20S found use in various professional fields:
- Aerospace Engineering: Used at NASA for quick calculations during the Space Shuttle program
- Financial Modeling: Employed by Wall Street analysts for complex financial calculations
- Field Engineering: Popular among oil field engineers for its durability and programming capabilities
- Academic Research: Used in physics labs for data analysis and statistical calculations
Collecting and Preserving HP-20S Calculators
For collectors, several resources are available:
- Museums:
- Computer History Museum in Mountain View, CA
- Heinz Nixdorf MuseumsForum in Paderborn, Germany
- Online Communities:
- HP Calculator Forum (hpcalc.org)
- Vintage Calculator Collector groups
- Reddit’s r/calculators community
- Documentation:
- Original HP-20S Owner’s Manual (available as PDF)
- HP Journal articles from the late 1980s
- Patent documents (US4837766 covers some HP-20S technology)
Conclusion
The Hewlett Packard 20S Scientific Calculator represents an important milestone in calculator history. Its combination of RPN and algebraic entry, robust programming capabilities, and durable construction made it a favorite among engineers, scientists, and students during its production years. Today, it stands as both a valuable collector’s item and a testament to Hewlett Packard’s engineering excellence in calculator design.
For those interested in experiencing the HP-20S today, emulation software provides an excellent way to explore its capabilities without needing to acquire an original unit. The calculator’s design principles continue to influence modern scientific calculators, particularly in the areas of user interface design and programming functionality.