Comparison
 Sperry-Remington 661-D |  Hewlett-Packard 35 (2) | |
| Manufacturer: | Sperry Rand Corporation (USA) | Hewlett-Packard Corporation (USA/Singapore) |
| OEM: | CASIO Computer Co. Ltd. https://www.qualityreplica (Japan) | |
| OEM model: | - | |
| Mfg. date: | 1973 | 1972-75 |
| Size: | 8×15,4×4,1 cm | 8×14,5×3,3 cm |
| Weight (ready for operate): | 330 g | 240 g |
| Type: | four-function | scientific |
| Capacity: | 6 digits (input/display) 6 (12) digits (internal precision) | 10/10+2 digits (input/display) 10/10+2 digits (internal precision) |
| Operating logic: | algebraic | RPN |
| CPU: | Hitachi HD32154P + NEC uPD129C | HP 1820-1169 |
| Registers: | 2 standard (with saving the pending operation) | 4 standard 1 memory (without arithmetic) |
| Features: | Fixfixed-point notation: the listed decimals can be chosen (0, 2) | +/-change sign (direct entry of negative numbers) RVexchange registers (X-Y) Ffloating-point notation Sciscientific (exponential) notation 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: | 6 digit VFD (6×NEC LD8085E) | 15 digit LED (HP) |
| Power: | 4×AA-type battery 6V adaptor | 3×AA-size NiCd battery pack |
| Test results: | trigonometry:result of sin-1(cos-1(tan-1(tan(cos(sin(60°)))))), reference value: 60. 60.00102632 exponential:result of 0.999160000, reference value (first 14 digits): 3.0068804206375×10-70 3.006896579E-70 |