Replica of MK-54 soviet calculator.
Based on sources of emu145 project: https://code.google.com/p/emu145/

See wikipedia for more information:
    http://ru.wikipedia.org/wiki/%D0%9C%D0%9A-54
    http://en.wikipedia.org/wiki/Elektronika_B3-34

Keypad:
              e1  e8

    c1  c2  c3  d2  d7

    b1  b2  c4  d3  d6

    a1  b3  c5  d4  d5

    a2  b4  c6  c7  c8

    a3  b5  b6  b7  b8

    a4  a5  a6  a7  a8