The HP 35 Then and Now

Prior to 1972, surveyors relied on books of tables, mechanical calculators, slide rules, and hand calculations to calculate anything they needed to know. The 'big deal' to surveyors was that the HP35 included the trig functions and storage registers. It also had a hard-to-read LED display, but we shaded it in the sun and didn't care. The books of sines and cosines to eight decimal places and nearest second sat in the back of the truck. The book we used to look up tangents (Peters) was left in the office. Instead, we carried little notebooks of keystrokes to follow for each type of calculation. Notably, the HP35 was handy for surveyors, but students couldn't afford it.

In the ensuing years surveyors have looked to Hewlett-Packard for the latest technology in programmable calculators to work with. We went through the HP45, HP65, HP67/97 (these latter two had built-in card readers, allowing the user to program them), and finally the HP41. The 41 kept evolving, with the final HP41CX (expected by HP to have a life of about three years). It lasted 14 years of production, and those who still have working 41s won't give them up. Students could afford them too, since the prices came down as the functionality went up.

Hewlett-Packard had very low-cost application pacs for the 65, 67, and 41, one of them being a Surveying Pac, which locked HP in as the surveyor's calculator of choice. Then came the HP48 and the advent of third-party software, in several updated versions, ending with the HP48GX (graphic expandable). Calculators got better and cheaper; the software for surveyors was extremely expensive, in several price ranges (none of them low).

We've arrived at a point where surveyors are paying whatever it takes to buy used HP48s on eBay. If the calculator can't be replaced, you're stuck with software that, in some cases, cost over $2,000 and won't work in anything else. The current calculator is the HP50g, 15 times faster than the 48, very affordable, and with reasonably priced software available.

A Tip on Changing Batteries in All Calculators

When you get a low-battery warning, do not try for "one more answer"; turn it off . Wait about five to 10 minutes before you try to change batteries and have the new batteries ready. Replace them one at a time, never taking them all (in this case both) out at once. After replacing them, again leave the calculator off for about five to 10 minutes to let the power level out.

Okay, the surveyors are covered for field calculations, but what about the students?

The HP33s was introduced a couple of years ago, and what made it exciting to surveying and engineering students was that it also qualified for use on the NCEES tests, and it was programmable. It is a little weird looking for an HP, and you have to program it by hand, but it is easy enough. Limited in programming with only 26 program labels and 26 storage registers, it used to be far better to do the tests with it than without it. Best of all, it was fine to work with in the classroom, and by the time you needed it for the Fundamentals of Surveying or Engineering test you were much more familiar with it as a tool than you would have been if you hadn't had to type in the programming by hand.

The HP35s: the New Star of Low-Cost Calculators

This calculator has essentially everything the HP33s had and a lot more, at about the same price. This one can even store coordinates as part of what you can program; it has 800 added storage registers, accessible through indirect addressing.

Professionals and college students have a flexibility no other scientific calculator can offer with the choice of RPN (reverse polish notation) or algebraic entry-system logic. This calculator is completely programmable; you can work more efficiently with its keystroke programming and handle the heaviest workloads with ease using 800+ independent storage registers plus 30 KB of memory.

You can include equations or expressions in your programming or store an equation and then use it again and again to solve any variable using HP Solve, or use 100 built-in functions. The equation actually runs like a program, prompting for each variable and calculating the unknown one.

The HP 35s has a large two-line alpha- numeric display with adjustable contrast similar to the HP33s and a robust library of built-in functions and constants. The two-line display makes it easy to view entries, results, menus, and prompts. (By the way, the programs can prompt for next-needed values or use prompts to branch with. For instance, you've calculated your curve data and now you're prompted to choose between staking out the curve or calculating another one.)

For other (required) classes, simplify physics with 42 built-in physical constants, plus a complete library of unit conversions. Get accurate results with the edit, undo, and delete capability. Use strong statistics functions for single and two-variable statistics, linear regression, and more. Perform operations on complex numbers, calculate logarithms, exponentials, and inverse functions; and take advantage of a powerful fraction mode plus fraction-to-decimal conversion, base-n functions for binary, octal, decimal, and hexadecimal number calculation and conversion. Statistic calculations, standard deviation, linear regression? Use the complete set of statistical registers. Yep, they made everything easier. And faster.

Using the HP35s in the Classroom and the Field

NCEES does not allow calculators that have a QWERTY (typewriter type) keyboard, infrared transmit/receive port, stylus, or pen input screen, etc. You have to keep it simple. Hewlett-Packard is working with NCEES to allow the new HP35s calculator for the exams, and they expect it to be approved, but maybe not in time for the remaining 2007 tests (the allowable list of calculators for the 2007 tests was issued by NCEES in 2006).

I've also been asked if it is tough enough for field use. It's a sturdy calculator in a solid case, has raised edges around the keypad to protect the keys, and comes with a zippered, hard carrying case. The calculator is held in the case with a well-placed elastic band, and HP did a great thing: the case has two elastic bands so you can mount the calculator for left-handed use.

The environmental limits make it usable in most regions, with an operating temperature from 32°F to 113°F and storage temps between -4°F and 149°F. It can also withstand 90 percent humidity at 104°F maximum. Battery life is pretty good, and it turns itself off after 10 minutes of non-use to help extend power.

About the Author

Ted J. Kerber has been a licensed surveyor since 1970 in several states, currently in private practice in California. He's been a survey instructor, lecturer, and author, and he's chief programmer and writer for Software by D'Zign.

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