The Casio J-1 is a large desk-top sized calculator from 1978 that fits in the hand. It is also known as the J-811. This model has a two-piece cream and dark brown plastic case with a brushed aluminum keyboard surround printed with black text. It features large square keys with typical Casio black plastic keycaps that provide a squishy but functional feel. The slightly tilted neutral display filter provides a clear view of the 8-digit vacuum fluorescent display. A raised panel on the front has a silver printed Casio logo and model name that has survived well on this example.
This calculator runs on 2 AA batteries or can use an optional AC adapter. It measures approximately 98mm x 159mm x 25mm and weighs 152g without batteries.
The J-1 provides basic four function arithmetic with percentages, sign change, square root, and three register memory. Switches allow selecting fixed decimal place settings and round-up protocols.
Internally, the J-1 uses a NEC D1877C processor and NEC LD8191 display tube. The keyboard connects to the main circuit board via 21 stiff copper wires. Accessing the interior requires squeezing and popping open the very stiff plastic case, which is quite difficult without damage.
Some quirks in the logic include:
- The C button clears the current number entry, while AC clears everything
- Overflow is suppressed on number input
- Divide by zero just displays E and cannot be recovered
- Storing values in memory provides no visual indication
- Sign change cannot be used mid-number entry
- Square root of negative numbers is allowed without error
- Negative numbers are limited to 7 digits using a minus sign
- Changing sign of an 8 digit number truncates it to 7 digits
Overall the J-1 provides a large format desktop calculator in a portable size. However, the logic issues noted above undermine its usefulness. This model appears nearly identical to the Casio J-3 released around the same timeframe.