MK 5021C - 10-digit calculator, 6 function (+, -, x, /, %, SQRT)

 
 Keyboard Matrix: 
         KN   KO   KP   KQ
    D1   1    +    dp1
    D2   2    x    dp2
    D3   3    �    dp3
    D4   4    -    dp4
    D5   5    +=   dp5
    D6   6    -=   dp6
    D7   7    +/-  dp7
    D8   8    =    dp8
    D9   9    .    dp9
    D10  0    CE   dp0  K
    D11  %    C
 

Notes: D11 is for entry error, overflow indication.
Columns KP and KQ are for static switches.
dp# selects a fixed decimal position, otherwise floating point.
Matrix positions -=, +/-, and K all require a diode in series with the switch, with the cathode connected to a column (KO or KQ) line.
The SQRT key requires three diodes, one in a static position between D4 and KQ, with the cathode connected to KQ, and two diodes with their anodes connected to D6 and D7, the cathodes tied to one side of the SQRT key, and the other side of the SQRT key connected to K0.

 
                        D4 ----->|------------------KQ
                        
                        D6 ----->|---+
                                     +----[SQRT]----KO
                        D7 ----->|---+