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Philips P-251 Printing Calculator Advertisement

Advertisement for Philips P-251 calculator

The Philips P-251 was the entry-level calculator in Philips P-25x-series of electronic printing calculators. The P25x-Series calculators. Philips, headquartered in Holland, had experimented with electronic calculating machines during the early to mid-1960's, and actually developed some interesting prototype calculators, but the machines remained Research & Development prototypes and did not actually made it to market. Had Philips pursued the idea of marketing a practical electronic calculator, the company could have potentially got a good head-start on some of the early players in the calculator marketplace, but for whatever reason, they did not market a machine until the 1967 timeframe, which put them a few years behind companies already in the marketplace by that time, including Canon, Casio, Sharp, Friden, Wang Laboratories, Monroe, Smith Corona Marchant (SCM), IME, and Sumlock Comptometer. As it turned out, Philips was never much of a force in the North American electronic calculator marketplace, but did experience some success in European markets.

The Philips P-251 was, compared to the competition in the printing electronic calculator market, actually quite advanced, using a dot-matrix printing mechanism that made it both fast, and quiet compared to other printing electronic calculators of the time. This method of printing was the first application of dot-matrix printing technology in an electronic calclator. The P-251 utilizes small-scale integrated circuits for its logic and magnetic core memory for storage of its working registers. This combination of relatively advanced technolgy, with the unique printing mechanism, made the machine very reliable and also quite fast. Along with reliability and speed, the P-251 was also quite reasonably priced at around $1,995. Other calculators with printing capabilities at the time typically sold for over $2,000.

The P-251 provides fourteen digits of capacity, with fixed decimal point output at 0, 1, 2, 3, 4, 6, or 8 digits behind the decimal point, set by a thumbwheel switch on the keyboard panel. During entry, there may be as many digits behind the decimal point as desired, within the fourteen digit capacity of the machine. Results of calculations are automatically rounded/truncated and printed using the 5/up, 4/down rule. The machine provides the standard four math functions along with a percentage function. The P-251 provides a single store/recall memory register that can be useful for storing partial results of more complex calculations. Despite the use of non-volatile magnetic core memory, the calculator's registers are automatically cleared at power-on, including the memory register, so no numbers are retained during times the calculator is powered off.

Philips' "Mosaic Jet" printing mechanim uses seven solenoid-actuated pins arranged in a vertical column, with the printhead on a carriage that can move freely across the width of the paper. The carriage is cycled left and right across the paper by a helical shaft that acts to shuttle the printhead back and forth across the paper. A wheel with a photographic mask of dark and transparent lines is attached the the carriage drive mechanism such that it serves to tell the electronics the position of the printhead at any given time by the logic counting the interruptions in a beam of light that shines through the photo mask. The action of moving the carriage is controlled by electro-magnetically actuated clutches that couple the rotary motion of the main drive motor to the helical shaft that moves the printhead carriage. The logic of the calculator commands the solenoids to fire at the appropriate times, driving the selected pin(s) into the ribbon, printing a dot on the paper. The pins are driven at just the right times to form the digits and annotations to be printed. This mechanism is simple, elegant, fast, quiet, has lots of room for manufacturing tolerances, and requires no special maintenance.