The Binatone is a basic handheld calculator from 1975. This one is model # 02-4252. It measures approximately 80mm x 145mm x 28mm and weighs 154g without batteries. The calculator is powered by 4 AA batteries or can use an AC adapter connected through a socket on the top side.

The case consists of two matt plastic pieces in dark and light blue. The upper area has grill-like slots resembling old desktop computers that needed ventilation. Below this is a black metallic sticker with the Binatone name. The display filter is neutral plastic with a silver painted border. The recessed keyboard area has a silver panel with an embossed power switch label. The keys are large with a short, loud click action.

The display is an 8-digit green vacuum fluorescent unit, with a 9th digit for negative numbers and error codes. When not in use, the display enters power save mode, showing only the 9th digit. Pressing a key brings the full display back.

The calculator offers basic four function math with percentages. It can handle 8 digit negative numbers shown with a minus sign in the left digit. Input overflow is suppressed, ignoring extra digits. Overflow in calculations shows an error code in the 9th digit but is recoverable. Divide by zero gives a similar error.

The logic includes an automatic constant feature on all four functions. However, it suffers from a “pseudo fixed decimal” bug – if you enter a decimal number, it becomes fixed at that number of decimal places until you use multiplication or division.

Inside are common 1970s components like the Texas Instruments TMS0851 chip, an Itron vacuum fluorescent display, transistors, diodes, capacitors and resistors. The keyboard connects to the main circuit board with short wires.

Overall, the Binatone 02-4252 is a sturdy, easy to use calculator typical of the mid-1970s. It has a pleasing blue color scheme and just enough features for basic math. The pseudo fixed decimal bug shows the limitations of early calculator engineering. But it remains a solid example of vintage portable calculation.

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