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  2. Mental calculation - Wikipedia

    en.wikipedia.org/wiki/Mental_calculation

    For example: 24 x 11 = 264 because 2 + 4 = 6 and the 6 is placed in between the 2 and the 4. Second example: 87 x 11 = 957 because 8 + 7 = 15 so the 5 goes in between the 8 and the 7 and the 1 is carried to the 8. So it is basically 857 + 100 = 957.

  3. Fuller calculator - Wikipedia

    en.wikipedia.org/wiki/Fuller_calculator

    The Fuller calculator, sometimes called Fuller's cylindrical slide rule, is a cylindrical slide rule with a helical main scale taking 50 turns around the cylinder. This creates an instrument of considerable precision – it is equivalent to a traditional slide rule 25.40 metres (1,000 inches) long.

  4. Calculator input methods - Wikipedia

    en.wikipedia.org/wiki/Calculator_input_methods

    The simplest example given by Thimbleby of a possible problem when using an immediate-execution calculator is 4 × (−5). As a written formula the value of this is −20 because the minus sign is intended to indicate a negative number, rather than a subtraction, and this is the way that it would be interpreted by a formula calculator.

  5. Divisibility rule - Wikipedia

    en.wikipedia.org/wiki/Divisibility_rule

    Most numbers do not divide 9 or 10 evenly, but do divide a higher power of 10 n or 10 n − 1. In this case the number is still written in powers of 10, but not fully expanded. For example, 7 does not divide 9 or 10, but does divide 98, which is close to 100. Thus, proceed from +,

  6. Slide rule - Wikipedia

    en.wikipedia.org/wiki/Slide_rule

    The pocket-sized Hewlett-Packard HP-35 scientific calculator was the first handheld device of its type, but it cost US$395 in 1972. This was justifiable for some engineering professionals, but too expensive for most students. Around 1974, lower-cost handheld electronic scientific calculators started to make slide rules largely obsolete.

  7. Casio V.P.A.M. calculators - Wikipedia

    en.wikipedia.org/wiki/Casio_V.P.A.M._calculators

    V.P.A.M. is similar to the Direct Algebraic Logic (D.A.L.) used by Sharp in some of their scientific calculators. The fx-82ES introduced by Casio in 2004 was the first calculator to incorporate the Natural Textbook Display (or Natural Display) system. It allowed the display of expressions of fractions, exponents, logarithms, powers and square ...

  8. Difference engine - Wikipedia

    en.wikipedia.org/wiki/Difference_engine

    A difference engine is an automatic mechanical calculator designed to tabulate polynomial functions. It was designed in the 1820s, and was first created by Charles Babbage . The name difference engine is derived from the method of finite differences , a way to interpolate or tabulate functions by using a small set of polynomial co-efficients.

  9. 1 + 2 + 3 + 4 + ⋯ - Wikipedia

    en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E...

    The nth partial sum is given by a simple formula: = = (+). This equation was known to the Pythagoreans as early as the sixth century BCE. [5] Numbers of this form are called triangular numbers, because they can be arranged as an equilateral triangle.