This period saw a gradual development of the mechanical calculator mechanism, great improvements on that of the first calculators
In 1902 the Dalton adding-listing machine was introduced. Unlike the early first calculators, this was the first of its type to use only ten keys, it became the first of many models of "10-key add-listers" manufactured by a variety of companies.
In 1948 the miniature Curta calculator, was introduced after being developed by Curt Herzstark in a Nazi concentration camp. This was an extreme development of the stepped-gear calculating mechanism that was hand held.
From the early 1900s to the 1960s, mechanical calculators dominated the desktop computing market). Major suppliers in the USA included Friden, Monroe, and SCM/Marchant. Unlike the first calculators, these devices were motor driven, and had movable carriages, the results of the calculations were displayed by dials. Most keyboards were full , so each digit that could be entered had its own column of nine keys (1 to 9), plus a column-clear key which permitted entry of several digits at once. Full keyboards usually had ten columns, however some lower-cost machines had eight.
Addition and subtraction were performed in a single operation in these machines, as on a conventional adding machine, whereas multiplication and division were reached by repeated mechanical additions and subtractions. The first calculators Friden produced, provided square roots by doing division but, with an additional mechanism which automatically incremented the number in the keyboard in a systematic fashion. The first of the handheld mechanical calculators for example the 1948 Curta continued to be used until the 1970s where they were displaced by electronic calculators.
The Facit, Walther, and Triumphator calculators are typical European machines. Machines with similar aesthetics included the Odhner and Brunsviga. However these are operated by hand cranks, but unlike the first calculators, there were motor-driven versions. Most machines that look like these use the Odhner mechanism or a variation of it. The Olivetti Divisumma had four basic functions of arithmetic, and had a printer. Full-keyboard machines, including that of motor-driven ones, were also used in Europe. Some European machines even had as many as 20 columns in their full keyboards.
The development of electronic calculators
In the late 1940s and 1950s, the first main-frame computers were developed, firstly using vacuum tubes and then later using transistors in logic circuits.
In 1954 , IBM demonstrated a large all-transistor calculator and by 1957, the company released the first commercial all-transistor calculator, in the IBM 608. However it was housed in several cabinets and cost around $80,000.
In 1957 The Casio Computer Co., released the Model 14-A calculator, this was the world's first all-electric "compact" calculator. It did not use electronic logic however it was built into a desk and used relay technology.
In 1961 , the world's first calculator that was 'all-electronic' was announced; the Bell Punch/Sumlock Comptometer ANITA ( A N ew I nspiration T o A rithmetic/ A ccounting). This machine used vacuum tubes, Dekatrons and cold cathode tubes in its circuits. It had 12 cold-cathode "Nixie"-type tubes for a display. From early 1962 , two models were available, the Mk VII for continental Europe and the Mk VIII for Britain and the rest of the world. The Mk VII was an earlier design with a more complicated mode of multiplication, it was soon dropped in favour of a much simpler Mark VIII version. The ANITA used a full keyboard, similar to that of mechanical Comptometers of the time, it was a feature that was unique to it and the later Sharp CS-10A amongst electronic calculators. Bell Punch had produced key-driven mechanical calculators of the Comptometer type under the names "Plus" and "Sumlock", and by the mid-1950s had noticed that the future of calculators was in electronics. The company employed the young graduate Norbert Kitz, to lead the development and the ANITA sold extremely well, as it was the only electronic desktop calculator available.
In 1963 the tube technology of the ANITA was replaced by the Friden EC-130, this had an all-transistor design and a 13-digit capacity on a 5-inch CRT. This model also was the first calculator to introduce reverse Polish notation (RPN) to the calculator market for $2200, this was about triple the cost of an electromechanical calculator of the time. Friden like Bell Punch, was a manufacturer of mechanical calculators, but they decided that the future lay in electronics.
In 1964 more all transistor electronic calculators were developed and introduced: Sharp introduced the CS-10A; this weighed 25 kg and cost 500,000 yen (~US$2500); and Industria Macchine Elettroniche of Italy introduced the IME 84, to which several extra keyboard and display units could be connected to, so that several people could make use of it, however could not all at the same time.
In 1965 saw the introduction of the Olivetti Programma 101, it was a stored program machine that could read and write magnetic cards, it also could display results on its' built-in printer. Memory could be partitioned between program steps, constants, and data registers due to an acoustic delay line. Programming could also be overlaid by reading from magnetic cards and allowed conditional analysis and programs. This model is regarded as the first personal computer produced by a company (ie a desktop electronic calculating machine that could be programmed, by non-specialists for personal use).
In 1967 the Monroe Epic programmable calculator came on the market. It consisted of a large, printing, desk-top unit, with a connected floor-standing logic tower. The machine was capable of being programmed to perform many computer-like functions but, the only branch instruction was an implied unconditional branch (GOTO) at the end of the operation stack, which returned the program to its starting instruction. So, it was not possible to include any conditional branch logic. The absence of the conditional branch during this era was often used to distinguish a programmable calculator from that of a computer.
In 1967 Texas Instruments developed the first calculator that was handheld. It was able to add, multiply, subtract, and divide. Paper tape was the output device.