Electronic "Slide Rules"


by John Frye

New pocket-sized electronic calculators are a big hit with both students and traveling business executives.

THE October morning, crisp as a potato chip, had everyone in a happy mood. Matilda hummed to herself as she dusted her desk prior to starting the day's work at Mac's Service Shop. The humming expressed her contentment and also served to drown out Barney's off-key rendition of "September Song" emanating from the service department.

The front door opened and Mac, her employer, came in carrying something in a small leather case. He uttered not a word but deposited the object on her desk, unzipped the case, and with a flourish removed a little black-and-gray instrument with a compact colorful array of white, blue, and red keys on top. "Now," he said, "don't say I never buy you anything!" "Gee, thanks; but what is it ?" "It's a miniature electronic calculator called the Compet ELSI-8, or EL-8 for short, made by Sharp Electronics in Japan but distributed in the U.S. by its Paramus, N.J. office.

I know you're going to love it. Here, lift it. It weighs only a fraction over a pound and a half and is 63/46" long, 4" wide, and 2 3/4" thick." "Where is the line cord?" "That's one of the beauties of it. It operates on six self-contained 0.450 A /hr rechargeable NiCad batteries or on a.c. with this little adapter-charger," he explained, taking another little leather case from his pocket and removing a small black box measuring about 2" X 2" x 4 ". A line cord came out one end and a coiled cord with a special plug on the end came out the other.

"So what can it do to replace Humperdink in Matilda's affections?" Barney asked as he came through the door of the service department.

Mac flipped a little switch on the side of the case of the calculator and instantly an eight-digit display of bright green numerals appeared behind the tinted, sloping, rectangular window at the top of the instrument. The numbers on the right kept changing rapidly and a negative sign appeared at the top of the window. Mac punched a key marked C, and the numbers stopped changing. He punched the key again, and the negative sign was extinguished and all the digits became zeroes.

"Now we're ready for business," he announced. "Give me some numbers to add." "Six dollars plus three dollars and fifteen cents," Barney offered.

Mac pushed a key marked 6, and instantly the right-hand 0 became a 6 with a decimal behind it. Then he pushed a Plus-Equals key, which had no effect on the display. But when he punched 3, the 6 disappeared and was replaced by a 3 with a decimal behind it. Pushing a blue key marked with a decimal did not change the display, but when the 1 was pushed the 3 and its decimal moved one place to the left and was replaced by a 1. Pushing a 5 moved both previously displayed numerals another space to the left, and the 5 showed up in the right-hand spot. Finally Mac pushed a Plus-Equals key, and instantly the display changed to 9.15.

"Hm-m-m, not even any kachunk, kachunk sound," Barney observed. "But I've got some questions. How come you didn't have to punch out a decimal and two zeroes on that six dollars? You did punch in the decimal on the three dollars and fifteen cents." "That's part of the Floating Decimal feature," Mac explained. "As long as you're keying a whole number, no matter how many integers make it up, the decimal stays put on the extreme right behind the last integer displayed. But if you hit the decimal key before keying an integer, the decimal moves left along with that integer. Watch what happens when I punch out pi." He hit the C key to clear the machine and return all displays to zeroes, and then punched out 3.1416. Sure enough, the decimal marched left step by step behind the 3 as successive integers were keyed. "And the decimals line up for addition no matter how many integers appear to the right and left of those decimals in the numbers being added. Now you see why I didn't have to hit the decimal and two zeroes when I recorded six dollars." "I assume it subtracts, too," Matilda said.

"Of course. The operation is only a little different. To subtract 3 from 9, you simply hit 9 first and then the Plus-Equals key, like so. Then you punch 3 and the red Minus- Equals key. There is your 6 answer. Continued subtractions require only that you punch out each subtrahend and then hit the Minus- Equals key to get the new remainder. If you wish, you can mix addition and subtraction by hitting the Plus-Equals or Minus-Equals key, respectively, after each number you wish to add or subtract. If, say in balancing your checkbook, the 'minuses' exceed the 'pluses,' the negative sign lights up to indicate that the number displayed reveals how much you are overdrawn; and it stays lighted as long as the displayed number is really negative." "Can it multiply and divide ?" Matilda pursued.

"It sure can. Suppose we want to multiply 9 by 3. I punch 9, hit the Times-Divide key, punch 3, and hit the Plus- Equals key, and there is the answer, 27, clear to the right.

Now let's go backwards and divide 27 by 3. I key in 27, hit the Times-Divide key, and punch 3. Now watch closely as I hit the red Minus-Equals key." The 3 disappeared from its place on the right and in the same instant a 9 followed by a decimal and seven zeroes appeared in the window.

"That display really flips from the right to the left side in a hurry," Barney said. "How fast does that thing work ?" "Addition and subtraction are performed in 20 milliseconds; multiplication in 150 miliseconds; and division in 200 milliseconds. But let me show you something else. Suppose we want to multiply 824005.1 by 930047.2. Notice I get an answer of 76636363." "Hey, that's too small an answer," Barney objected.

"Right you are. The complete answer is 7663636 36040.72. Notice the lack of a decimal on the right tells us the display is not a complete answer. The machine can handle eight digits multiplied by eight digits, but it can only display the first eight digits of the answer and discards the rest. This is called the Underflow System. However, it does keep track of the decimal beyond the eight displayed integers and the decimal can be recalled into the display by multiplying by 0.0000001, as I do now. See, our display now reads 76636.363. Since the decimal was called back seven places, we know it actually belongs four places to the right of the last integer in the original answer, which can be rounded off as eight significant figures and four zeroes." "I see Alarm and Error printed on the display window. What are they for ?" Barney asked.

"A green dot appears besides the Error sign and the display goes to all zeroes and only the C key will function when the integral number result in multiplication and division exceeds 16 digits, if addition and subtraction calculations are performed continuously when the decimal is not displayed, or when the battery voltage becomes too low to insure accurate performance.

When the last happens, you connect the Adapter-Charger and throw the switch to AC. This powers the instrument and trickle-charges the battery at the same time. In 12 to 15 hours of this type of operation, the battery will be recharged. It can be quick-charged in 3 hours with the charger connected and the instrument switched Off. A red indicator lamp on the charger goes out when the battery is fully charged, but the batteries are protected against overcharge. If the instrument is connected to the charger but is switched to DC instead of AC, a red dot appears beside the Alarm sign to warn the operator the battery is not being charged." "How long does a charge last ?" Barney wanted to know.

"About three hours." "Is the C key just used to clear the machine ?" Matilda asked.

"No, it's also used to delete a mistaken entry. When I was adding 3.15 and 6, if I had accidentally keyed 3.16, I could have hit the C key and the 3.16 would have disappeared and the display gone back to 6. Then I could have proceeded as before." "I don't suppose it will handle powers and roots," Barney hazarded.

"Not directly, but a set of common logarithms, such as I just happen to have with me, reduces power and roots to multiplication and division, which the instrument can handle. For example, suppose you wanted to find 2.82415. You multiply the logarithm of 2.82, which is .4502, by 4.15, like so, and get 1.86833. The antilog, 73.84, is your answer. Or suppose you need the fifth root of 1.251. The logarithm is .0972. Dividing by 5 we get .01944.

Your answer is the antilog, or 1.0458." "How can so much smart math be wrapped up in such a small package ?" "Chiefly by the use of Extra Large Scale Integrated circuits, of which this instrument has four. Notice its name comes from the initials. Each ELSI measures only ' /A" square but does the work of 1875 resistors, diodes, capacitors, etc." "I'm afraid to ask, but what does that thing cost ?" Barney questioned.

"Three-hundred and forty-five dollars complete with adapter /charger." "Does anyone but Sharp make them ?" "Oh yes. Sharp was the first, but lots of other companies, chiefly Japanese, are getting into the act. These include such firms as Canon, Sanyo, Busicom, Hitachi operating through the Frieden Division of Singer, Monroe Division of Litton Industries, Commodore Business Machines of Toronto, etc. Some of these are 12- and 16-digit machines that display six or eight digits and view the rest through a lens system. Others provide a paper print-out in addition to the light display. The ELSI-8 uses mini fluorescent display tubes, but others are trying LED's and liquid-crystal displays. Competition is fierce; lightning advances in microcircuitry are being snapped up; low-cost solid-state keyboards have been developed; there has been overproduction in some areas; and such widespread price-cutting that the Japanese are working toward an export cartel to establish a minimum price structure for calculators produced for overseas markets." r "I get the idea Japan is pretty big in the calculator business." "Very big. In fact, Japan produces 70% of the world's calculators and exports half of this. The U.S. took 40-50% of the $181-million worth of calculators exported last year and is Japan's best customer. On the other hand, we manufacture most of the integrated circuits used in the calculators. North American Rockwell has a $30-million contract with Sharp for advanced MOS/ LSI circuits. Texas Instruments makes them for Canon. Mostek Corp. of Dallas supplies MOS chips for Busicom.

General Instrument makes LSI chips for Sanyo." "Well," Barney said, patting the little instrument, "I certainly forecast a bright future for these devices, especially if the price keeps coming down.

Think how handy one would be for a college kid taking engineering. It is almost as portable as a slide rule and is faster, more accurate, and keeps track of the decimal. It can add and subtract, which a slide rule can't." "I'd like to take it with me when I'm buying groceries," Matilda admitted.

"Actually, it could be all the calculator most professionals or small businessmen would need. But now will you two lugs go on back into the service department and let Elsie and me become acquainted? After all, I thought you bought this calculator for me!"

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