Non-HP RPN (Reverse Polish Notation) Calculators
	Sinclair Scientific. Introduced in 1974, One of Sinclair's two RPN calculators. Hewlett Packard had introduced the HP 35 with advanced scientific functions at that time, but at a very high price. Of course, the HP was of superb quality, while the Sinclair was fragile. Original price: £32.50 built, or £19.95 as a kit.
	Sinclair Scientific Programmable. Introduced in 1975, this was British Sinclair's answer to programmable calculators. The price was low, but so was the functionality. The reason this calculator made it to this collection, is because it used RPN. Original price: £25
	Commodore Minuteman 6X. This is a plain four-function calculator manufactured by Commodore in 1973. However, it is the only Commodore calculator that was manufactured with RPN logic. Commodore also manufactured the exact same calculator as the Minuteman 6 (not 6X) with algebraic notation.
	Calfax 616. I cannot locate any information on this calculator other than that Calfax was a division of American Imports Merchant Corporation and most likely manufactured in Hong Kong in the mid-70s. It remains interesting as another example of an RPN calculator however. It also sold under the label Supercal 616.
	Omron 12SR. Manufactured by Omron Tateisi Electronics of Japan, they had colorful buttons and displays. The 12SR, also known as "the slide rule," is the only RPN calculator Omron manufactured. It has a green fluorescent display with all the standard scientific functions.
	National Semiconductor 4520 Scientist. An RPN calculator manufactured by National Semiconductor, USA, which also sold calculators under the Novus name (see below).
	National Semiconductor 4525 Scientist PR. Another RPN calculator manufactured by National Semiconductor, this one a programmable one.
	National Semiconductor 4640. Another RPN calculator manufactured by National Semiconductor.
	National Semiconductor 4615 PR. Also an RPN calculator manufactured by National Semiconductor in Malaysia in the 1970s. Identical to the Novus Mathematician PR. It is a scientific programmable calculator with 102 steps.
	National Semiconductor 600. Introduced by late 1973, this is a simple RPN calculator, however without an ENTER key. The "+" key is used in place of ENTER to separate numbers. Original price: $19.95
	Novus 650 "Mathbox". Introduced in 1974 by National Semiconductors, it could do the basic four arithmetic operations. It is of great interest however, as it like Hewlett Packard, was using the RPN notation, instead of the common algebraic notation found in most calculators. Original price: $17
	Montgomery Ward P10. This is a Novus 650 "Mathbox" (see above), but with the Montgomery Ward brand on it. It is functionally equivalent to the 650.
	Novus 4510 Mathematician. Also known as the Novus 4510 or the National Semiconductor Mathematician, it was a National Semiconductor calculator branded as Novus to help them promote their calculators. Like the Hewlett Packard calculator, it uses the RPN (Reverse Polish Notation) method to perform calculations. It was introduced in 1975 and was manufactured in Malaysia. Original price: $60
	Novus 4515 Mathematician PR. Another National Semiconductor RPN calculator, also known as the NS 4515. This one, however, has a 3-level stack and it is programmable.
	Privileg SR54-NC. A scientific RPN calculator made by Quelle International, W. Germany. It basically has the same engine as the Omron 12SR (notice the "SR" notation on both).
	APF Mark 55. APF Electronics Inc., a New York city based calculator manufacturer, had most of their models built in Japan. Mark 55, built in 1977, was the only APF with RPN logic. It included, like the HP, a 4-level stack named x, y, z and w, 9 memories and the basic scientific and statistical functions, along with some unit conversions. Original Price: $60
	Elektronika B3-19M. The first Soviet Elektronika RPN calculator manufactured in 1976. Included basic scientific functions in a very robust case, but with keys that were light to the touch and could very easily produce erroneous entries. Original price: 240 rubles
	Elektronika B3-21 (LED). One of the first Soviet Elektronika calculators, the production of which started in 1977 and ended in 1981. It was an RPN calculator, programmable with 60 steps. The early version used red LEDs. Original price: 350 rubles
	Elektronika B3-21 (VFD). This is the second version of the B3-21 that used a green VFD display. It has otherwise the same functionality of the original model, but was offered at a reduced price. Original price: 190 rubles
	Elektronika B3-34. A Soviet RPN calculator, the production of which started in 1978-1979. A very popular calculator, it included scientific functions, 98 program steps and indirect addressing. It also used a green VFD display like the B3-21. This design was later changed to create the MK-54 (see below). Original price: 80 rubles
	Elektronika MK-54. A Soviet RPN calculator, most likely the first one in the series of MK calculators. Production started in 1982 and stopped in 1985, possibly because the more powerful MK-61 was in the mean time released. Original price: 65 rubles
	Elektronika MK-52. This calculator was made in Russia between the years 1983 and 1991. A true RPN and programmable calculator with 105 steps and 15 memories. It was the only calculator in the world to use EEPROM (512 steps) for internal storage of data and programs. It had a Cyrillic keyboard. Original price: 115 rubles
	Elektronika MK-61. One of the most powerful (non-BASIC) Soviet calculators ever manufactured, it also had a Cyrillic keyboard and was also an RPN calculator. It is identical to the MK-54, but the MK-61 is programmable capable of accommodating 105 steps and 15 registers. Production started in 1983 and finally stopped in 1993. Original price: 85 rubles