Commodore SR4190R

The Commodore SR4190R calculator, introduced in 1976, is from Commodore’s scientific calculator line. It was manufactured in England but most of the parts were made in Japan. It retailed for $79.95.

The SR4190R boasts a large, tilted case made from textured black plastic, with a heavily inset, tilted red plastic display filter. This design provides a clean, bright image, although the viewing angle is somewhat narrow. The calculator features bold colored keys in red, blue, green, grey, and white, which are small and have a squishy, wobbly feel. The top section of the calculator has a raised brand name painted silver.

Powered by a 6V sealed rechargeable battery pack consisting of three AA-sized cells, the SR4190R can also be powered using an adapter/charger through a socket located at the top middle of the device. Compatible adapters include DC640, 707, 708, or 709, all operating at 6 Volts with a center-positive configuration. The calculator weighs 220 grams with batteries and 152 grams without, making it portable yet sturdy.

The display of the SR4190R is a 10-digit red LED module with a bubble lens, including an eleventh digit for the minus sign. Additionally, there is a smaller 2-digit red LED module for the exponent, also featuring a bubble lens and a third digit for the minus sign. This setup allows for clear and precise readings, even in varied lighting conditions.

In terms of functionality, the SR4190R offers over 80 functions, including Poisson and Gaussian distributions, integrals, derivatives, probability calculations, and conversions between various units such as Fahrenheit to Celsius, ounces to grams, gallons to liters, miles to kilometers, and BTU to Joules, among others. The calculator also features two memory storage registers, although they are not permanent.

The SR4190R is equipped with a whopping 49 keys. The logic of the calculator is sound, providing extra precision, although it lacks recovery from errors and constant function capabilities, which can be somewhat inconvenient.

The internal components of the SR4190R include a MOS MPS 7200 5177 CPU, two ITT 546A-SN 7625 display drivers, two GHU-01A ESR keyboard decoders, a 10-digit LED module, resistors, a diode, capacitors, a transistor, a voltage regulator, and a 3AA-sized Ni-Cd rechargeable battery unit made by Saft in France. The calculator is densely packed, with three boards connected by a thick ribbon cable, making disassembly and reassembly challenging.

Logic:

• The (C/CE) button clears the last entry of a number when pressed once and clears the entire calculator when pressed twice.
• Overflow on number input is suppressed; typing an eleven-digit number ignores the eleventh digit.
• An overflow error is indicated by an “E” in the eleventh digit, whether negative or positive, and is not recoverable.
• Dividing by zero results in an “E” error, which is also not recoverable.
• There is no constant function available.
• There is no indication of memory storage; users must remember stored values.
• Hours, minutes, and seconds are displayed with a “-” between them.
• Negative numbers are indicated by a “-” sign in the eleventh digit, allowing for full ten-digit negative numbers.
• Calculations are precise to 12 digits.
• The change sign function can be used mid-number entry.
• Upper functions are accessed using a two-key stroke system: press the (F) key first.

The Commodore SR4190R offered a wide range of scientific functions which made it a reliable tool for students and professionals at the time.