## HP 35s Calculator Annoyances III

I keep saying how much of a fan I am of the RPN mode, and have used it on and off since high school. But times have changed, and HP needs to find a way to manipluate the logic of repeated calculations to make RPN still come out on top, but I feel discouraged, and feel there is no turning back.

I’ll tell you why. For one thing, you can’t enter any calculation in a mode involving stacks and operators, which is at the heart of RPN logic, and expect it to repeat without some way of remembering each operator and number you pressed. And the only way to do that is to really learn how to program this calculator, then preferably bind the program to a key. So, this is really not a calculator for sissies. At least, not unless you stay in algebra mode.

There was one more thing that I don’t think I’ve mentioned: viewing numbers in scientific notation sometimes requires you to use the scroll feature. This is because it will show you as many as 12 digits, pushing the power of 10 exponent off the immediate display.You need the left arrow to see what you missed.

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## HP Calculator Annoyances II

I am as much of a fan of the RPN mode as anyone. But the implementation of RPN in the HP calculators have to keep up with new developments in technology.

For one thing, I had trouble in RPN mode, to make a list of random numbers. Suppose you wanted to make a list of numbers with a certain variability such as:

`150 + 25*RAND`

I would do this to generate a list of random numbers with a minimum of 150, and a maximum of 175. RAND is the random function which generates a number between 0 and 1. In RPN, I would need to enter 150 and 25 in a stack, then my RAND, then * and then +.  That generates one such random number. To generate more numbers, such as a list of 25 numbers, you need to go through the whole thing again, 24 more times. It may have been necessary 20 years ago to actually repeat the same keypresses over and over like this, but dual displays have been around for slightly longer than 20 years, making these operations a lot less error prone, and way more efficient.

You may do this calculation better in algebra mode, using the left arrow key to go back to the statement you typed in, then press ENTER to get the new number. This will cause fans of RPN to vascillate back and forth between algebra and RPN modes whenever they need to take advantage of certain features. It is likely that the official HP claim that RPN is more efficient with respect to key presses is becoming less and less true as technology improves, unless HP can figure out how to repeat a stack of numbers and operators.

More on this next Wednesday.

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## More on the HP 35s Calculator

I have kept some notes as I was performing an stats operation on a list of numbers. Most of the time the interface on most calculators is intuitive enough that you don’t really need the manual to do things like stats or common operations on the scientific calculator. The Sharp calculator has data entry for stats refined to the point where you can return to any list member and correct the entry.

Stats on the HP35s is of the “old school” variety, with an important change: the calculator is always in single variable stats mode. Hitting the “Sigma+” key on the bottom of the keypad is enough to begin your entry, and this means you can interrupt your data entry at any point and to any other calculation that you need to do. This is true in both RPN and Algebra mode.

One annoying feature I found is that if you have a syntax error, there is no “clear error” or “clear” button that will instantly remedy it. All attempts to clear the display have to be done through a “clear” button that is made as a second function to the backspace key (the backspace key is the other way to clear your error, one character at a time, using the arrow keys to help you). To clear everything (“clear/all”) requires you to go through 2 layers of menus.

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## What is old is new: RPN on the HP 35s Scientific Calculator part 3

For those of you lucky enough to purchase the calculator back in 2007, you more than likely had the full 200-page print edition of the user manual. HP discontinued the print edition, possibly later that same year. It has been replaced by a smaller 40-page mini manual whose only real useful purpose has been to help me review the main points of RPN. If you are a beginner, then you need to access the full manual which is now stored on CD. My CD, which I bought less than a week ago, appears to have been last updated in 2009. The same CD also has the same manual in 15 other languages.

You would have had the ability to review the book at your leisure, rather than on a laptop screen the way I have to view it. It is a bit of a deterrent and is tiring on my eyes, but I guess it beats having no book. I have discovered that you can purchase copies on E-Bay if you feel desparate enough for a print copy. You will probably shuck out your dollars for a print copy if you want to program, or if you want to have a more through mastery of its system of menus.

However, if you program, it must be stated quickly that much of the programming language is printed on the keyboard above the keys, and are active in program mode. It is definitely a caclulator that had its keyboard laid out with the programmer in mind, and with their needs as the higher priority. A look at the keypad shows a lot of programming commands rather than statistics, summations, or clearing the stack, all of which require menus. The “STO” function requires the blue shift key to be pressed first; and the functions for x2, log, ln all require a shift key to be pressed first. For whatever reason that perplexes me, there seemed to be a need to cram a good fraction of the interface of the calculator with various conversions: metric to imperial, fraction to floating point, degrees to radians, signed to absolute value. It takes up 10 of the 43 keys. Since none but grade-school calculators have these conversions, I am not sure of the motive. It is likely that it helps in the programming to save coding effort.

It seems to be all about the programming. Programming takes up 5 chapters or 100 pages of the 382-page booklet. Plenty to learn for the HP 35s programming enthusiast.

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## What is old is new: RPN on the HP 35s Scientific Calculator part 2

I saw the 35s for the first time in a Staples store just this year, though the calculator has been around in University bookstores since 2007. I bought mine on sale, being listed at \$99.00 full price. When it came out in 2007, I heard that it came with a zippered pouch to store the calculator in. Mine, supposedly the 2011 model, came with a vinyl pouch that was open, with rather stiff elasticized cloth bands on the sides, making the calculator difficult to actually place in its pouch, especially the first time it was used.  Once in the pouch, it was difficult to take back out of its pouch. The calculator feels light when held in one’s hand. I’m not sure why I noticed that. Somehow I thought it would feel more substantial, given all of the functions and programmability, and the 800 or so memories that it boasts of.

2012 will be the 40th anniversary of the scientific calculator. HP made the world’s first scientific calculator in 1972, and it was an RPN calculator with no algebraic mode. Anyone who has tried to program in a serious way would appreciate that RPN is easier to program for (from the manufacturer’s point of view), because of its reliance on a memory model called “stacks”, which most computer science undergraduates know about, by second year at the latest. While the act of doing things algebraically might seem easier to us humans, programming a calculator to think in terms of human algebra is more difficult than you would think. It takes a computer many more steps, and thus it is much slower than RPN in terms of processor time. It was probably not until the early 1990s that calculators were capable of anything close to human-style algebra, and only recently have processors become so small and fast that the speed of the algorithm is not really as important as it used to be. But human speed might be. To those who take the time to understand how RPN works, and how the 35s implements stacks, RPN is still faster for humans to perform calculations.

Many of the features on the 35s are common on much cheaper calculators: statistics, regression, vectors, mixed fractions, complex numbers, numerical integration, numerical differentiation, a linear solver, and there are much cheaper calculators that can solve single-variable polynomials up to order 3. I own a \$5.00 calculator that can solve linear systems in up to 3 unknowns. Also, there are too many features on the “new” HP 35s that are tied up in menus, which is something that turned me off from using TI calculators. The only tangible attraction I can think of for this calculator is likely to be its programming mode. The 35s is among the very few non-graphical calculators around today that one can write programs in.

Playing with it a bit, I find that scientific notation seems to work up to 10500, meaning the computation of factorials can go to unheard-of extremes, even going beyond the capacity of an Excel spreadsheet. I was able to find, to several sig figs, the value of 253!, wheras Excel 2007 craps out past 125!. This means that this calculator is particularly powerful for performing permutations (nPr) and combinations (nCr).

I have lost my touch with the use of stacks from my programming days, but it looks like the calculator does a lot of pushing and popping, even in the middle of the stack. In addition, it only seems to perform calculations on the stack 2 at a time, even though the stack can accomodate 4 numbers. When you enter numbers, it’s like “pushing” numbers on to the bottom of the stack. You enter a number, and the stack moves up. If  you enter two numbers then add them, the stack moves down and the result of the addition is entered in the immediate register in the stack, called “x”.  The true implemtnation of this is that, for the registers t, z, y, and x, t gets its number copied to z, z copies to y, and y copies to x. This results in a duplication of t in the stack. If a “+” is pressed when a stack contains the numbers “1 2 3 4”, it adds only 3 and4, then the top 2 registers shift down and the result of adding 3 and 4 is placed in “x”: “1 1 2 7” becomes the resulting stack. The “1” and “2” shift down, but in reality, the memory register values are just copied.

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## What is old is new: RPN on the HP 35s Scientific Calculator part 1

When I comment on technology, I like to discuss the good and the bad about it. I don’t sell calculators, and I don’t get freebies to review. That gives me the freedom to freely comment.

One has to admit that for HP to sell a \$90 RPN calculator in this age of \$20 textbook display calculators takes guts, especially if said \$90 calculator does not have graphical capabilites. HP has been making RPN calculators since the 1970s. In the 80s, they had their heyday when their top-of-the line calculators not only had programmability, but even came with complex functions stored on cards on which was mounted a piece of magnetic tape on the small plastic card which one would swipe through a reader inside the calculator. Every key including the number key seemed to have at least 3 functions, and usually 4.  It was a great technology, but the calculators were quite pricey, but loved by statisticians, university professors and math nerds everywhere.  The common theme in all of these calculators was that their input was required to be in reverse Polish notation, or RPN.

In RPN, you enter your two operands, and press the button for the operator last. This requires an “Enter” key; and since the calculation is over once you press the operator, there is no need for an equal sign. In fact, the keypads are noted for their lack of an equal sign.

On a normal calculator, entering “2 + 2” is a matter of entering the operands and opereator in the order you would write them down. For RPN, you enter “2 2 +”, hitting an “Enter” button after each “2”. The advantage of RPN, to those who have the patience to give themselves such a habit of thought for this, is that the overall effect is that you can do a reasonably complex calculation with fewer keystrokes, than on a conventional calculator. And while it promised efficiency, it was never a calculator for button monkeys. To take advantage of  RPN’s efficiency you always needed to think carefully about the calculation. But I must state that HP is ready for today’s generation: they do in fact, provide an “algebraic” mode where it uses the common algebraic syntax you would expect on most other calculators, but on my calculator, it was RPN that was the default.

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