Swapping Display Memory on Desk Calculator

v.1
\[\begin{array}{llll}
math.&{key\\presses}&{DISP.\\B}&{MEM\\A}\\
M=M+D & [\ M+\ ] &B&A+B\\
D=-D & [\ ±\ ] &-B&A+B\\
D=D+M & [\ +\ ]\ [\ MR\ ]\ [\ =\ ] &-B+A+B&A+B\\
M=M-D & [\ M-\ ] &A&A+B-A\\
M ↔ D &done&A&B
\end{array}
\]

v.2
\[\begin{array}{llll}
math.&{key\\presses}&{DISP.\\B}&{MEM\\A}\\
D=-D & [\ ±\ ] &-B&A\\
D=D+M & [\ +\ ]\ [\ MR\ ]\ [\ =\ ] &-B+A&A\\
M=M-D & [\ M-\ ] &A-B&A-A+B\\
D="0,=" & [\ 0\ ]\ [\ =\ ] &0(+A)&B\\
M ↔ D &done&A&B
\end{array}
\]

v.3
\[\begin{array}{llll}
math.&{key\\presses}&{DISP.\\B}&{MEM\\A}\\
D=D-M & [\ -\ ]\ [\ MR\ ]\ [\ =\ ] &B-A&A\\
M=M+D & [\ M+\ ] &B-A&A+B-A\\
D=D-M & [\ -\ ]\ [\ MR\ ]\ [\ =\ ] &-A+B-B&B\\
D=-D & [\ ×\ ]\ [\ 1\ ]\ [\ -\ ]\ [\ =\ ]\ \left({\ _{[\ =\ ]}\ }\right)^{\ (1} &(-A)·1-((-A)·1)&B\\
M ↔ D &done&A&B
\end{array}\\
_{NOTE^{\ (1}\ :\ DEPENDING\ ON\ THE\ SPECIFIC\ CALCULATOR\ THE\ ALTERNATE\ SEQUENCE\\ FOR\ THE\ ARITHMETIC\ NEGATION\ [\ ±\ ]\ MAY\ REQUIRE\ DOUBLE\ [\ =\ ]\ PRESS} 
\]

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