The Citizen 831RD calculator, introduced in the late 1970s, is a robust and versatile calculator designed for both desktop and handheld use. Manufactured by Citizen Business Machines Inc. in Japan, this calculator is notable for its distinctive design and reliable functionality.
The calculator’s dimensions are approximately 86mm in width, 165mm in height, and 22mm in depth, making it somewhat larger than typical handheld calculators of its time. However, its wedge-shaped design ensures a comfortable grip, and its size makes it well-suited for desktop use as well. The Citizen 831RD is powered by a 3V DC, 2 x AA size rechargeable battery pack, and it also accepts an adapter/charger through a socket on the top side.
The case of the Citizen 831RD is made from a two-piece light grey smooth plastic body, with a prominent dark grey battery pack on the top that slides off with the batteries intact. The back of the calculator features an embossed diagram illustrating how to remove the battery pack. The display is tilted slightly and has a green filter, providing a bright and clear view of the digits. The keyboard surround is made of brushed aluminum with black printed text, and the keys are designed with a squishy, long-travel feel that is both responsive and aesthetically pleasing.
The display of the Citizen 831RD is an 8-digit green Vacuum Fluorescent Display (VFD), with a ninth digit reserved for indicating negative numbers, memory usage, and error messages. The calculator offers standard four-function capabilities, including percentages, change sign, register exchange, square root, squares, reciprocal, and a four-function memory. Additionally, it features a switch for defining floating, 1, 2, or 4 decimal points.
Logic
- (CE) is used to cancel the last number entered.
- (C) clears the entire calculator.
- Automatic constant is available on all four functions.
- Input overflow is suppressed; inputting a ninth digit is ignored.
- Negative numbers are displayed with a “-” in the immediate left digit, allowing full eight-digit negative numbers.
- Divide by zero shows “o” in the upper section of the far left (ninth) digit and is not recoverable.
- Overflow shows the result with “o” in the leftmost (ninth) digit and is not recoverable.
- The change sign can be used mid-number entry but is not always necessary as the minus key can be used before multiply and divide.
- Memory store is indicated by an “r” in the upper section of the far left (ninth) digit.
- Negative square roots are not allowed but show the result, which is unrecoverable.
The Citizen 831RD calculator is a well-designed and functional tool that offers a range of mathematical operations suitable for various applications. Its unique design, including the prominent battery pack and tilted display, sets it apart from other calculators of its era. While it lacks overflow recovery, its logic is sound, and its components are robust, making it a reliable choice for both handheld and desktop use.
