--- title: HP 27S description: HP's first algebraic scientific calculator, of 1988, with a solver for your own equations, its history, what makes it special and how saturnus runs it. section: models model: 27s --- The HP 27S is a scientific calculator that Hewlett-Packard introduced in January 1988. It was HP's first scientific pocket calculator with algebraic entry instead of RPN. It has no programming: you type your equations into a solver instead, and it adds money calculations, a clock and appointments to the usual scientific functions. ![HP 27S](../img/27s-640.webp) The 27S as saturnus draws it, showing π. ## At a glance | | | |---|---| | Released | 4 January 1988, at $110 | | Discontinued | Between 1990 and 1993 (sources differ) | | Code name | Mentor | | Processor | Saturn core in HP's Lewis chip, about 1 MHz | | Memory | 8 KB RAM (about 6,900 bytes for you), 64 KB ROM | | Display | Two lines of 22 characters, 131 × 16 pixels | | Keyboard | 37 keys, one shift key, six menu keys | | Entry | Algebraic, with operator precedence | | Input and output | Infrared output to HP's 82240A printer, beeper | | Clock | Time, date and ten appointments | | Power | Three button cells | | Size | 148 × 80 × 15 mm | ## History ### Four calculators in one day On 4 January 1988 HP introduced four calculators at once: the 27S, the [17B](17b.md), the 19B and the [28S](28s.md). An electronics magazine reported in March 1988 that all four have HP Solve, which lets you enter equations without programming, and print by infrared to HP's 82240A printer. The 27S and the 17B were the first of HP's Pioneer series: slim calculators of the same case and keyboard, built around Lewis, a custom chip with an improved Saturn processor core. Wikipedia notes that the two share the same hardware inside. The [42S](42s.md) followed in October 1988. ### Algebraic at HP For years HP's scientific calculators had used RPN. The Museum of HP Calculators calls the 27S the first fully algebraic pocket scientific calculator HP made; the qualification is needed because HP had sold algebraic desktop calculators and computers before. Its algebra keeps pending operations in the display. Type 1 + 2 × 3 and you see the expression; type + 6 and the 27S works out what it can and shows 7 + 6. Functions of one number still come after it: you type 5 SIN, not SIN(5). ### A "do-everything" calculator The Museum of HP Calculators calls the 27S another "do-everything" calculator, after the first one, its namesake the HP-27. Like the HP-27, it cannot be programmed. Although called a scientific calculator, it has time value of money with loans, savings and amortization, date arithmetic, a clock and appointments. ### Price and end The 27S launched at $110. Finseth's data shows it at $80 by November 1990. When it was discontinued is not clear: the Museum says 1991, Finseth before 1993, and Wikipedia gives the range 1990 to 1993. ## What makes it special ### The history stack The calculator keeps four lines: the line you work on and the three results before it, which the manual calls the history stack. The display shows two of them, or one and a menu. The arrow keys scroll through it, and LAST brings the previous result into the expression you are typing. So even an algebraic calculator has a stack you can look back on. Operators follow precedence: in the manual's example, 4 + 9 × 3 = gives 31. The 17B, launched the same day, works in chain order instead. ### The solver instead of programs The SOLVE application stores your equations and solves each for any of its variables. Type an equation, and the 27S makes a menu of its variables: key in a number and press a variable's menu key to store it, or press the key alone to solve for that variable. The built-in applications' menus work the same way. Equations can share variables, so a value found in one is ready in the next. The manual's first example is free fall: enter the equation of motion once, then ask how far an object falls in 5 seconds or how long it takes to fall 500 metres. An equation can do more than arithmetic. The IF function picks between two expressions by a condition, and Wikipedia notes that sub-formulas, loops and conditional execution can be written inside formulas. Letters for names come from the ALPHA menu, which Finseth lists as a first, shared with the 17B: a two-level menu of characters on the menu keys. ### The applications - Statistics with lists, and probability. - Time value of money, with loans, savings, leasing and amortization. - Number bases: binary, octal, decimal and hexadecimal. - Hyperbolic functions, angle, time and coordinate conversions, percentages. - The clock: date arithmetic and ten appointments, each with a message of up to 22 characters. When one comes due the 27S beeps; if it is off, it turns itself on to announce it. - Ten numbered registers, R0 to R9. ## In saturnus saturnus runs the 27S with ROM revision B: - It boots, computes, and the ROM check of its self-test passes. - "Set the clock" sets the 27S's clock to your computer's time, by pressing the keys of its TIME menu as you would. Appointment alarms have not been tested. - On your computer's keyboard, F1 to F6 press the menu keys and Escape is CLR. - The CPU runs at 1 MHz, the figure the sources give for its chip. No timing of a real 27S has been measured to check it against, so run times are an estimate. 2×, 4× and Max speed it up. - Save and load states work as on every model. What it does not do: the 27S has no serial port, so Files has nothing for it, and the infrared printer output is not emulated. The memory view and the RPL editor are for the HP 48 and 49 only. The [command reference](commands.md#27s) lists the 27S's 251 functions with the keys that run them, and examples for 60 of them, run in saturnus. [Open the HP 27S in saturnus](../app/#/calculator/27s) ## Sources - [HP 27S Owner's Manual](https://literature.hpcalc.org/community/hp27s-om-en.pdf): the history stack, precedence (4 + 9 × 3), variables in menus, the Solver and its free-fall example, IF, about 6,900 bytes of memory, the applications, appointments. - [Finseth's HP calculator data: HP 27S](https://www.finseth.com/hpdata/hp27s.php): dates and prices, code name, entry logic, the first Pioneer and the two-level ALPHA menu, display, processor, power, RAM and ROM. - [Museum of HP Calculators: HP-27S](https://www.hpmuseum.org/hp27s.htm): the first fully algebraic HP scientific, pending operations in the display, LAST, the HP-27 as the first "do-everything" model, the features, years. - [Wikipedia: HP-27S](https://en.wikipedia.org/wiki/HP-27S): years, size, the shared hardware with the 17B, the keyboard of the Pioneer series, formulas with loops and conditions, ten appointments. - [Wikipedia: HP-28 series](https://en.wikipedia.org/wiki/HP-28_series): Lewis as a custom chip with an improved Saturn core. - [Electronics & Technology Today, March 1988](https://archive.org/details/ElectronicsTechnologyToday1988-03): the four calculators launched together, HP Solve and infrared printing.