Citizen 820SR
Brief History
Citizen's range of calculators consisted of OEM versions of the most successful Japanese products of that era. Ise Electronics — the later Systek, which is not the same as the Ise company that manufactures display tubes — produced more or less identical models for continuously increasing number of customers. We can find the simpler, four-function machines among full-featured scientific models in Citizen’s 800 series. The 820SR is the entry-level scientific calculator; the A4001 integrated circuit made by Rockwell, which was also the first integrated circuit for scientific calculators, was made for machines that compete with Hewlett-Packard’s calculator (HP-35), but was much simpler and much cheaper. A year later, Citizen could claim a much wider range of models; because at that time Rockwell and other companies also offered several types of integrated circuits for those building scientific calculators.
| Manufacturer: | Citizen Business Machines Inc. (Japan) |
| Mfg. date: | 1974 |
| Size: | 8,8×15×3,4 cm |
| Weight (ready for operate): | n.a. |
| Type: | scientific |
| Capacity: | 8 digits (input/display) 8 digits (internal precision) |
| Operating logic: | algebraic |
| CPU: | Rockwell A4001PC (15471) |
| Registers: | 2 standard (with saving the pending operation) 1 constant (with saving the pending operation) 1 memory (with aritmetic) |
| Features: | +/-change sign (direct entry of negative numbers) RVexchange registers (X-Y) Ffloating-point notation BSbackspace (right-shift) function Sqrsquare root pivalue of pi (3.1415..) can be recalled 1/xreciprocal trigtrigonometrical functions (sin, cos, tan and inverses: arcsin, arccos, arctan) logexponential and logarithmical functions (10- and e-base) yxraising to power |
| Display: | 8+1 digit VFD (Futaba 9-CT-02) |
| Power: | built-in 4×AA NiCd and battery charger/adaptor |
| Test results: | trigonometry:result of sin-1(cos-1(tan-1(tan(cos(sin(60°)))))), reference value: 60. 62.57928 exponential:result of 0.999160000, reference value (first 14 digits): 3.0068804206375×10-70 0 |
820SR
Inside of the 820SR
Keyboard of the 820SR
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