The Detson 803PM calculator, manufactured in 1976, is a compact device that fits comfortably in the hand, thanks to its smooth, rounded edges. It measures approximately 72mm in width, 123mm in height, and 20mm in depth, and weighs a light 102 grams without batteries. The calculator is powered by a 3V DC, 2 x AA size rechargeable battery pack, with the option to use an adapter/charger through a socket on the bottom right side.
The Detson 803PM is housed in a two-piece gloss finish brown plastic case, which may not be to everyone’s taste. The case features an oversized green display filter that enhances the brightness of the display. A small metal label, printed in black with the company and model name, sits in its own recess. The keyboard surround is made of brushed aluminum, with the “on” label printed in black. The keys, although small and squishy, are functional and responsive.
The display is an 8-digit green Vacuum Fluorescent Display (VFD), with a ninth digit for negative, memory, and error indication. The calculator offers standard four functions with percentages, change sign, square root, pi, and a three-function memory.
The original case is made of soft black plastic with an open top and half-moon cut-outs, sharing the same design as the Decimo Vatman Mini M. The calculator is composed of several components, including an NEC µPD278C H5Z076 CPU, a 9-digit VFD with a round face, a transistor, five diodes, six capacitors, seven resistors, two resistor arrays, and a transformer. The keyboard assembly floats on top of the main CPU board and is held together with ten screws. It is connected to the main CPU board via a 15-way ribbon cable. Disassembly is challenging and not recommended due to the risk of damaging the calculator.
Logic
- (C/CE) is used to once cancel the last number entered and a second time to clear the whole calculator.
- There is automatic constant on multiply and divide only.
- Input overflow is suppressed, inputting a ninth digit is ignored.
- Negative numbers are shown with a “-” in the far left (ninth) digit thereby allowing full eight-digit negative numbers.
- Divide by zero shows “C” in the far left (ninth) digit and is not recoverable.
- Overflow shows the result with “C” (or “E” if negative) in the left most (ninth) digit and is not recoverable.
- The change sign can be used in mid-number entry.
- Memory store is indicated by the decimal point of the far left (ninth) digit.
- The (MRC) key is used once to recall the memory and a second time to clear it.
- Negative square roots are not allowed and result in “C” with zero result.
The Detson 803PM calculator is a reliable device with sound logic, although it lacks recovery features and certain constants. It is a compact calculator and is easy to hold with its smoothed edges. Most Detson’s are collectible.
