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Category: Calculators
Tags: Calculator Hp-50g

HP-50G and RPN

Reverse Polish Notation is a blessing. Unfortunately there are only a few calculators on the market which are able to perform calculation in RPN... historicaly there were number of models produced by HP for the consumer market which could be operated in RPN; such calculators have long since lost their market share, so now it seems the only option is to buy second-hand. Even worse, these superior machines have lost their grip on the market (or perhaps, never found it to start with) thanks to the increasingly well-groomed calculators from Texas Instruments.

That's not to say that TI's calculators are good; actually they're quite bad, but that's only to say that companies like College Board endorse their shitty calculators while actively discriminating against higher-functioning HP equivalents for being too "computationally functional" and "powerful".

That's right, HP's calculators are so good that TI and College Board wants them erased from the market; that's (more or less) what's been happening over the past 40 years, and in chasing its waning market share HP has found it necessary to compromise its consumer calculators and make decisions which give a touch of accessiblity (i.e. make them easier to understand) for the modern consumer (i.e. dolt) but these decisions hinder calculation speed and efficiency. Fortunately HP has left the existing modes in their newer calculators for you to toggle, which I would highly recommend you do. First a little exposition.

THE HP-50G is a Calculator

First, the HP-50G is a calculator: yes. It fits into a carrying case and has all the little buttons on it so categorically yes: it is a calculator.

Next: the HP-50G is a computer: also yes. Do not let anyone convince you otherwise. There is nothing the HP-50G cannot already do which a computer can also do. A so-motivated person could port Fortnite to the fucker. Because it is a computer.

Reverse Polish Notation

The HP-50G supports an input method called Reverse Polish Notation. It is much simpler than the algebraic input method we are accustomed to.

Consider the following problem:

21+((10*30)/(7+8))

On a typical algabraic mode calculator (i.e. a TI8* or on an HP-50G in algebraic mode, the default mode), one would need to enter the following ridiculous string of inputs

21 + ( ( 10 * 30 ) / ( 7 + 8 ) )

Now consider an RPN calculator; this kind of calculator uses a well-known paradigm called a stack to track of the arguments to arithmetic operations. Once a user has pushed arguments to the stack the user may operate on them by pressing the appropriate operator on his / her calculator. The above problem may be tackled on an RPN calculator with the following inputs.

21 [ENTER] 10 [ENTER] 30 [ENTER] * 7 [ENTER] 8 [ENTER] + / [ENTER] +

[ENTER] pushes the entered number to the STACK; notice that operators do not require an [ENTER] because operators operate on elements on the stack. The stack is first-in last-out (i.e. FILO order) so an binary operator will apply the input operation the most recently pushed items on the stack, then the result will be pushed to the stack. Unary operations (like square-root) operate only on the most recently pushed element on the stack (i.e. the element at the "top" of the stack). Subsequent operations may then be applied to the result of the previous operation, as it is now an element on the stack. One can read more about RPN (and the various flavors of it) on the HP Museum website.

As lamented earlier, the HP-50G factory-default (for the benefit of the consumer who is confused by RPN) is algebraic mode, which means that calculations take more keystrokes because one does not benefit from the advantages of having a running STACK. I encourage users who have a calculator capable of being put into RPN to actively use it. In addition to saving keystrokes, things like vector operations, matrix multiplications, and complex arithmetic become effortless. This is explored further in an eletrical-engineering context, but the results are applicable to all fields which demand the use of complex algebra and matrix operations.

HP-50G is a power-engineer's best friend

While the HP-50G is a wonderful calculator for personal finance, party tricks and fast arithmetic, the HP-50G has demonstrated its worth for me as a companion for solving problem sets relating to power-engineering and the mathematical analsyses of generators and motors. Because these fields are essentially heavy-handed applications of vector and matrix arithmetic, having a calculator which makes both of these things trivial to input and compute simplifies the problem set and allows me to focus on the more interesting concepts surrounding power distribution grids and their mathematical equivalent models.

For instance, consider phasor notation. If one has a phasor voltage of 5 volts at an angle of 45 degrees, one may input that into the HP-50G as:

( 5 [RIGHT SHIFT] 9 3 45

The 9 and 3 preceded by [RIGHT SHIFT] will input a degree symbol; if anything, I wish that there was simpler method for inputting this but the esoteric [RIGHT SHIFT] 9 3 has become second-nature. Anyhow, this creates the phasorj which then may be pushed to the stack with ENTER and operated on.

Complex numbers may be treated in a similar fashiion. If I wished to input the rectangular-form equivalent of the above voltage, (that is, 3+j4 where j is sqrt(-1)),

( 3 [SPACE] 4

Now if one pushes that expression to the stack, something interesting will happen: the first and second input voltages will be of exactly the same notation: both elements on the stack will be represented on the display as either polar or rectangular format, using either degrees or radians or gradians. The displayed notation depends on the settings of the particular calculator. The point being that the notation will be the same; the fact we input them with different notations is irrelevant because they are converted at the time of input into the notation setting of the calculator.

This means that if one has (something like) 5 volts at an angle of 45 degrees across an impedance of 10+j20 it becomes trivial to find the current through such an impedance because the calculator takes care of the conversion for us. If after operation on these quantities one desires the results in the opposite notation, it is only requisite that we tell the calculator to do so in its settings (for the HP-50G this setting is in [MODE], but can also be accessed using [MATH] menu).

Sales Pitch

Basically if you value your time buy an after-market HP-50G or HP-49; they are almost the same calculator and both will save you time and energy and save you from the tyranny with which TI has run the "free" market of graphing and scientific calculators in 2010s.

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