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Appendix A: Design Concepts
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When you press  + , x is added to y, and the entire stack drops to display the answer in X. The same thing happens for –, × and ÷. Whenever the stack drops, t is duplicated from T into Z, and z drops to Y as follows:
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Press
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Contents
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Location
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+, –,
× or ÷
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Look at the contents of the stack as we calculate (3 × 4) + (5 × 6). The keys used are shown above the circled steps 1 through 9. Directly above the keys you see the information in X, Y, Z and T after the key stroke.
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T
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Z
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12.
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12.
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Y
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3.
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3.
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12.
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5.
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5.
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12.
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X
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3.
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3.
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4.
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12.
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5.
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5.
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6.
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30.
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42.
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KEY
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3
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SAVE
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4
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×
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5
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SAVE
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6
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×
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+
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STEP
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1
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2
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3
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4
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5
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6
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7
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8
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9
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Step
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Remarks
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1
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3 is in display (X)
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2
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3 is duplicated into Y.
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3
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4 is in display (X)
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4
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Contents of X and Y are multiplied; result (12) is loaded into X.
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5
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Automatic SAVE pushes 12 into Y when 5 is keyed in, display shows 5.
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6
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SAVE pushes 12 into Z, 5 into Y, and leaves X unchanged.
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7
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6 in display overwrites 5 in X since it immediately follows SAVE .
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8
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Contents of X and Y are multiplied; result (30) is loaded into X, 12 drops to Y.
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9
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Contents of X and Y are added; result (42) is loaded in X.
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