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Victor Comptometer 18-1721 Scientific/Engineering Electronic Calculator Advertisement

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Advertisement for the Victor Comptometer 18-1721 Calculator
Scan of Advertisement Courtesy of Norm N.

Presented is an advertisement for the Victor Comptometer Model 18-1721 Scientific/Engineering electronic calculator, offering this capable calculator for the rather low price for the time (late 1972) of $495. This low price was made possible by heavy use of Large Scale Integration integrated circuit technology, a microcoded compute engine, and commonality of parts shared across the line of 1800-series display calculators.

The Victor 1800 series display calculators included quite a range of calculators from a basic office calculator, such as the 18-1441, to the top-of-the line 18-1721 featured in this advertisement. All of the display calculators in the 1800 series utilized the same general architecture, with a Burroughs Panaplex planar display, a six-chip Rockwell-made calculating engine with one of the six chips containing the unique microcode that provides the specific functionality of the model of calculator.. The machines also share a common power supply, cabinet base, display driver circuitry, and keyboard design.

There were a number of print-only calculators in the 1800-series trading out the display for a printing unit that Victor purchased from European manufacturer Walther. The printing calculators in the series also shared a common design, with common cabinet, printer drive circuitry, power supply, and main logic board containing four of the same chips used in the display calculators, along with two chips that interface the printer, and a single chip containing the operating microcode for the calculator.

The Victor 18-1721 was specifically designed for scientific and engineering types of calculations, with a good variety of mathematical functions that would suit such work. The 18-1721 operates algebraicly, and provides automatic decimal point placement to optimize the accuracy of displayed results. Numbers are left-justified in the display eliminating un-needed leading zeroes, and unnecessary trailing zeroes are suppressed. Numbers containing up to fourteen digits can be displayed, with an extra two hidden guard digits maintained internally to provide better accuracy. The 18-1721 provides the standard four math functions, along with a single accumulator-style memory register, with the [M+] key adding the number in the display to the memory register; the [MC] key clearing the memory register, and the [MR] key recalling the content of the memory register to the display. The [π] key enters an approximation of the value of Pi within the limits of the calculator's precision into the display.

The [EX] key provides a convenient means to swap the operands in dyadic math functions, for example; entering 16 [÷] 2 [EX] [=] will give an answer of 0.125, which is the result of the division with its two operands swapped. The [CS] key toggles the sign of the number in the display, useful for entering negative numbers. The [C ALL] key clears the working registers of the calculator and the display, but leaves the content of the memory register intact. The [C] key is used to clear the display, primarily used to erase an incorrectly entered number allowing the correct number to be entered without disrupting any calculation in progress. The scientific/engineering functions include reciprocal [1/x], exponential [Xy], square root [√], and logarithm [LOG]. Also included are the three basic trig functions; [SIN], [COS] and [TAN]. An [INV] key is pressed before the [SIN], [COS], [TAN], or [LOG] keys to provide the inverse trig function along with anti-logarithm calculation. Two slide switches select the type of argument/result for the trig functions, providing settings for degrees or radians. The second slide switch selects the type of logarithm function performed, with selections for common (base 10) or natural (base e) logarithms.

The display utilizes a 9-segment Burroughs BR-16401 Panaplex planar gas-discharge display panel with sixteen display positions, of which fourteen are used for displaying numbers. The right-most position is used only for indicating a negative number by lighting a '-', and the left-most position used for indicating error conditions. The extra two segments are located vertically down the center of the digit cell to provide the ability to display the digit '1' centered within the display cell. The display is driven by a unique to the series display driver circuit board that is populated with Victor-proprietary hybrid circuit modules that contain the driver circuitry for the display panel. Each hybrid circuit module contains two digit drivers and a segment driver, incorporating a number of driver transistors and resistor networks onto a ceramic substrate, encapsulated in a tough ceramic-based packaging material. These hybrid modules are not serviceable. If the circuitry inside one of these modules fails, the only solution is to replace the failed module with a new one. That wasn't really problem, though it did require delivering the calculator to an authorized Victor service center and paying the inflated parts and labor prices to replace the failed part. The display drive modules were easily available in the early 1970's when the 1800-series display calculators were marketed. Today it is a different story, as these parts are unobtainium and haven't been manufactured for decades.. If one of these driver modules fails, either another Victor 1800-series calculator must be available to scavenge a module from, or one must get creative and have the skills to develop an equivalent circuit made from discrete components to perform the function of the failed hybrid module.

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