HP 35s


The HP 35s is a Hewlett-Packard non-graphing programmable scientific calculator. Although it is a successor to the HP 33s, it was introduced to commemorate the 35th anniversary of the HP-35, Hewlett-Packard's first pocket calculator. HP also released a limited production anniversary edition with shiny black overlay and engraving "Celebrating 35 years".

Features

The HP 35s uses either Reverse Polish Notation or algebraic infix notation as input.
Other features of the HP 35s include:
  • Two-line alphanumeric LCD
  • Over 800 memory registers and j, indirect addresses.
  • Scientific and statistical functions
  • Operation in decimal, binary, octal, hexadecimal
  • Equation solver with arbitrary variable isolation
  • Numerical integration
  • Support for input and display of fractions
  • Complex number and vector calculations
  • Unit conversions and table of physical constants
  • Keystroke programmability with approximately 30 kilobytes of memory for programs and data
The HP 35s has been given a retro look reminiscent of classic HP calculators from the 1970s to the 1990s. However, it provides far more functions, processing power, and memory than most of those earlier models.
The physical appearance and keyboard layout of the HP 35s is very different than that of its immediate predecessor, the HP 33s, but the two calculators are functionally very similar. The primary differences are:
  • The HP 35s allows both label and line number addressing in programs. The HP 33s had only label addressing. With only 26 labels, it was difficult to write programs making use of the entire 30 KB of memory.
  • The memory in the HP 35s is also usable for data storage, in the form of an extra 801 numbered memory registers.
  • Support for vector operations is new in the HP 35s.
  • Complex numbers are treated as a single value instead of two separate values.
  • Indirect branching, which allows the contents of a memory register to be used as the target of a branching instruction is omitted from the HP 35s.
  • No arbitrary limit to length of equations.
  • Algebraic mode uses typical infix notation.
HP has released a free-of-charge 35s emulator for the Windows operating system. This was previously only available to teachers for classroom demonstration purposes.

Construction

The HP 35s was designed by Hewlett-Packard in conjunction with Kinpo Electronics of Taiwan, which manufactures the calculator for HP in mainland China.
According to HP, the calculator has been engineered for heavy-duty professional use, and has been tested under extreme environmental conditions. It is built using 25 screws for rigidity and ease of maintenance.
The case features many design elements from 1970s HP calculators such as the ground-breaking HP-65, including a black case with silver-striped curved sides, slope-fronted keys, and gold and blue shift keys. The faceplate is metal, bonded to the plastic case. The key legends are printed, rather than the double-shot moulding used in the vintage models.
The calculator is powered by two CR2032 button cells connected in series, which it is advised to replace one at a time, to avoid memory loss.
It was initially supplied with a hard zippered clamshell case with a pocket for notes, and a printed manual, but this was later changed to a slipcase made of vinyl-covered cardboard with elastic sides and velvet lining, and a CD-ROM containing a PDF manual.
The calculator is entirely self-contained; there is no facility for upgrading the firmware, nor for loading/saving programs and data.

Reception

The build quality and industrial design of the 35s has been welcomed by reviewers as a return to design of the traditional HP calculators, with 4-Level RPN and RPN Programming. However the lack of built in matrix functionality, and cheaper plastic quality models, it was primarily marketed to the student market. Particular mention has been made of the traditional HP feel of the keyboard with a big key back in its traditional place. Shortcomings which have been identified include the lack of any facility for communication with a computer, and sluggish performance.
Response to the calculator's logic has been mixed. The increase in addressable registers and introduction of program line-number addressing have been seen as a big improvement over the 33s. While welcoming the improved handling of complex numbers compared to the 33s, the incomplete support for them has been criticised. Working with hexadecimal and other non-decimal bases has been criticised as requiring excessive and unintuitive keystrokes. Several firmware bugs have also been reported, which have not yet been fixed.
The 35s's lack of communication abilities makes it acceptable for use in some professional examinations where more powerful calculators would not be. For example, in the US, it is the most powerful programmable calculator approved for use in the Fundamentals of Engineering and Principles and Practice of Engineering examinations.

Feature details

Entry modes

The 35s supports both RPN and algebraic entry modes. Like most HP calculators, it defaults to RPN. The entry mode can be easily changed by the user. An annunciator on the display indicates the current entry mode.
In RPN mode, it uses a four-level stack, as have all HP's non-graphing RPN calculators since the earliest days. In contrast to the usual computer-science terminology, RPN calculators such as this refer to the operational end of the stack as the bottom and the far end as the top. The stack levels are named X, Y, Z, and T ; they have no connection with the variables of the same names. Level X appears on the lower line of the display and level Y on the upper line. Each stack level can contain any of the data types supported by the machine: real number, complex number, or vector. Various functions are provided for manipulating the stack, such as and to roll, to swap X and Y, to recall the last-used X value, and to swap X and a named variable.
Algebraic mode works by the user entering an expression, then pressing to have it evaluated. The expression appears on the upper line of the display, the result on the lower line. The expression can be edited using the arrow and backspace keys, and re-evaluated as desired.

Units and fractions

In keeping with the calculator's retro theme, conversions between Imperial/US units and the equivalent standard metric units feature prominently on the 35s's keypad. To facilitate those who still use traditional units, and for other uses, the calculator also allows the entry of values as mixed fractions and the display of values as mixed fractions.
Entry of mixed fractions involves using decimal points to separate the parts. For example, the sequence converts inches to 10.0 cm.
The calculator may be set to automatically display values as mixed fractions by toggling the key. The maximum denominator may be specified using the function. Numbered flags may be set to specify which of three denominator systems is to be used: most precise denominator, factors of the maximum, or a fixed denominator. Two small arrow symbols on the display indicate if the actual value is slightly above or below that displayed. There are no functions to directly extract the parts of the displayed fraction.

Complex numbers

Previous HP calculators have handled complex numbers in a variety of ways. In the HP 33s, complex numbers were stored as two separate values, and the "complex" modifier was used to indicate that an operation was to treat the stack as containing complex numbers. For example, adding and involved the following keystrokes:, which used up all four stack levels.
The 35s stores complex numbers as single values, which can then be operated on in the standard ways. The above example of adding and then becomes:.
On the 35s, the number of functions able to handle complex numbers is limited and somewhat arbitrary. For example, directly taking the square root of a negative real number results in an error message instead of a complex number. This is strictly correct given that a nonnegative real number a has a unique nonnegative square root and this is called the principal square root which is denoted by. The symbol √ is called the radical sign or radix. For example, the principal square root of 9 is 3, which is denoted by = 3, because and 3 is nonnegative. However raising x to the power of 0.5 using the key works if the number is entered as a real number with a complex part equal to zero. Inverse and hyperbolic trigonometry functions cannot be used with complex numbers. Base-e logarithms and exponentiation can be used, but not base-10. However, workarounds exist for many of those limitations.
Complex numbers can be entered in either rectangular form or polar form, and displayed in either form regardless of how they were entered. They can be decomposed using the and functions. There are no functions for extracting real and imaginary parts, though that can be worked around, using the formulas and.

Vectors

The 35s provides facilities for handling vectors of up to three real-number elements. A vector may be stored on the stack, or in any variable, as a single value, and processed by various functions. It is entered by the user starting with a square bracket, then the element values separated by commas. Vectors can be added, subtracted, multiplied and divided by scalars. Two vectors of similar dimensions may be added and subtracted, and multiplied to give their dot product. The function will return a vector's magnitude. A cross-product function is not available, nor any function to extract individual elements from a vector, but these can be readily calculated by the user.
Vectors can also be used to simply store up to three real numbers together, thereby increasing the calculator's storage capacity, though with more complexity and reduced speed. HP have published program code for the 35s which enables this.