ZENTREX Advanced Numerical SystemsII Inc.
ZTR-51/HperAdvanced Slide Rule+ Calculator
21st Century Power: 1970's Kitsch!

Weclome to the world of virtual fantasy vintage calculators. In the middle 1970's the pocket calculator was starting to be a common item. This was when the "slide rule" calculator came into being and the math, science and engineering geeks started grabbing them up and so did students now needed more than just the basic functions for things like Statistics class. I had one of the early ones: A Texas Instruments SR-50 and my best friend, going for a Doctorate in Physics at Brown University, had an HP of some kind that was programmable with RPN entry. Then they brought out the built-in subroutine. single-keystroke operations that set up the unit to do more than one calculation onces you put in the data. Things like Mean, variance and standard deviation all done in about 5 seconds, as well as other things and by 1977 we were off to the races.

Now I find that JavaScript Source has come down with one that is almost a spitting image of the TI slide rule jobs and Earthewb Javascripts has a boss RPN calc and both work in FireFox. With these little wonders, you can do things like perimeter, area, volume and conics calculations,trig functions, Engineering and Statistics, In the hands of a moderately competent person, these things are deadly. With my old SR-50 I've done two-way Analyses of Variance, Chi-square, Correlation and Regression, non-parametric statistics and post graduate statistics. Don't let the term "fantasy calculatro" mislead you into thinking that it is a non-working, inferior item or the product of some self-absorbed micro-mentality. Be rest assured that this is a professional level piece of gear and serious business. To make it easier to work with, I've color-coded it. You notice that the red area matches the name text in color, thoat's the "slide rule functions" section. You notice there's no % key. Well, these were made for the mathematically hip dudes who knew that to do percentages from fractions, you multiplied the fraction times 100/1 such that x/y*100/1= n%. If you were useing a decimal then you just moved the point two places to the right. thus X% was gotten from .x by moving the point two plalces over: .55=55% and like that. So a % key is for babies, although I do have a %age that includes % and the chain-calculations subroutine has it as a convenience. The same goes for the Pythagorean calculation. But this is no ordinary Pythagorean subroutine: How about a right triangle subroutine that can figure any side given the other two and let you know if you're trying to do an illegal operation? It was our business to know the formulae going in, these things were just high-power number crunchers but at that, they were nukes and even now will serve you well. The only difference between this little cutie and my SR-50 is that the MS key was "sto [store]" and MR was "rcl [recall]" and the battery pack and adapter, I'll make a gazillion spares of this. I also used my SR-50 to balance my checkbook and do accoutning. When it finally bit the bag for good and all, I cried.


This brings up the idea of fantasy retro calculators. Just as you have fantasy sports and the like, I see these as the "rules of the game"
  1. OPERATION: First and Foremost; before anything else, the thing has to work. Any idiot can draw pictures and play make-believe. However real fantasy is not make-believe. and this is not a make-believe prop. If you have a key that says "Fractions" There had better be a subroutine to add, subtrace, multiply or divide fractions. The same for number base conversions or anything. If you're gonna run your mouth, then you better run the math. Don't talk so big if you can't do the trig.
  2. APPROPRATE INTERFACE: You select a timeframe. The 51/H is a 70's style. Now, Software based calcs can look like anything, probably the "best" is the spreadsheet. However, I'm used to keys and buttons and that was the interface of a 70's pocket calculator. There is no law against doing a desk calculator, in fact, in 1973, my first experience was with a Wang tabletop calculator with which I fell in love and said "a pocket version of this would be great. I gotta have one!". You can do a more modern LCD version or even a "fairy-tale princess' calculator". The "Space Patrol Power console's Math & Science Console uses calculators in a "desktop' console" configuration. For the '70's, a black body and light-on-dark display screen best suits the style since the LCD dispaly did not come in until the late 1970's and did not really take over until the 1980's or 90's. Now, for the 51/H, the keys do call up a separate screen, but even some of the late '70's units had displays that were more than just numbers. We even provide the power switch, pilot light and just to show that it's a high-quality unit, the dreaded "battery check" with a half-brightness standby mode.
  3. MANUAL: These were standard fare in the 70's and were by no means thin, either. They explained things like operation, how to do specific types of caulculations like mean and were the repository for data and tables and therefore an integral part of working with the unit. However, since this type of calc has been around now, much of this kind of thing is pretty standard so that "n!" is pretty well understood as "n factorial[1x2x3x4...xn]" and "n things taken r at a time". At any rate, there should be some explanation and instruction. The manual should also be meaningful LIke those oldies but goodies, the 51/H has much of the material in the Appendices. I could have put table lookup in the unit proper but that would not do. The closest the real calcs had to tables in the calculator was one or two on the back, either glued on, painted or written in bas-relief. Since it is a virtual machine, some of the manual pages are intereactive I have two Periodic Tables of the Elemints; one is in the calculator as part of a subroutine and the better one is in the Manula. Also the Resistor table is intereactive but these were all I could get. But as in real life, you have to go to the back of the manual, and the RPN "Tutorial" is in the manual; right where it belongs. With more than fifty items, you will be using this manual plenty
  4. LIMITS: Since we're talking about fantasy calculators then there is a certain amount of "wiggle room". while a simulated LED display is mandatory and the manual has the same features as a real 1976 calculator manual. We may go a little over the top with a function or two that would never even be possible in the "real" thing. These limits are:
    • No anachronisms. Let us say I'm making a 'Fairy Princess" version of a 1972 calculator, subroutines would not be allowed, the display would be light on dark and I could probably get away with more than two but no more than four non-standard, non-mathematical functions (my two favorites would be a search engines page and an image search
    • No off-screen additional keypads. All the keys must fit on the main displays
    • Only one or at most two. off-the-wall functions. After too many of them, you start to de-nature the instrument.As propounded by Tolkien, fantasy is not simple wish-fulfillment or just making it up. It must still be an integrated, organized whole with no loose ends.
    • All the items in the manual must relate to the calculator
    Having done my first custom version, I came to an understanding of these principles of design.
  5. MANUFACTURER: Since this is a somewhat made-up thing and since cualculators were physical objects made by some company, you need a company. The company name ought to sound like something that fits with an appropriate logo, I showed an earlier model of this to a person who was not part of the science and technology culture and she said the name sounded like a cold remedy. Here's the skinny on that. In 1975, the proliferation of over-the-counter cold meds was in its infancy so that name would not have been around in that context. She was thinking of COMTREX, which was not around until c1980. One of the major scientific electronics companies was Centronics, "Zen" and "Cen" are enough alike to resonate with the cognicenti. "Zen" and "Tao [pronounced "dow"]" meant the "heart of a metter" as in The Zen of Motorcycle Maintenance. "TREX" can also be read as "TR-X", which has a kind of scientific aura. it can alsoe be tangential to Star Trek, which was enjoying a rennaissance at the time. Finally, there is the visual aspect; the First E is a "summation" operator (summation being recursive addition of the sort a+b=c+d=e+f....=z) and the second E is written such that it can be read as either E or -, which implies a bit of psycho-tech, which was also kind of big. So you get a nice logo. This whole incident was an adventure in how we are creatures of our culture. When I first heard "Dance of the Sugarplum Fairy" at age 10, I called it "sneaking-around music"; it sounded like the kind of music that would be used when someone is sneaking into or out of a place. Just the idea that there is music while someone is sneaking about shows how tied I was to the auio/video culture of radio, movies and television in the mid-1950's..
Since it is a fantasy calculator, there must be a bit of outrageousness to it, not to the point of over the top, but to the point that it stands out as a bit of wish fullfillment overlaid on something at least semi-realistic; it has to be out there but plausible. Since this is a fantasy math, science and engineering slide rule calculator like I would have killed for in '78. The emphasis is on "built-in" subroutines, which I found plenty of at the javascripts websites. Even the manual is the manual that I wish I had in terms of data tables, I doubt that there were any manuals nearly that thorough in the world of 1976.

So if you can't let go of the 1970's then grab hold of the ZTR-51/H! And with your purchase, you get an imaginary (the squar root of -4) two year subscription; 1975-77 to the Ayn Rand Letter. Such a deal: Ain'cha glad this is a freebie?! Wuddayawant for nuthin'; a rubber biscuit?