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| Case 1: exy > 0 and ex > ey |
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The principal axes are counterclockwise to the current axes (because exy > 0) and no more than 45º away (because ex > ey).
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| Case 2: exy < 0 and ex > ey |
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The principal axes are clockwise to the current axes (because exy < 0) and no more than 45º away (because ex > ey).
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| Case 3: exy > 0 and ex < ey |
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The principal axes are counterclockwise to the current axes (because exy > 0) and between 45º and 90º away (because ex < ey).
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| Case 4: exy < 0 and ex < ey |
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The principal axes are clockwise to the current axes (because exy < 0) and between 45º and 90º away (because ex < ey).
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| Case 5: exy = 0 and ex > ey |
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The principal axes are aligned with the current axes (because ex > ey and exy = 0).
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| Case 6: exy = 0 and ex < ey |
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The principal axes are exactly 90° from the current axes (because ex < ey and exy = 0).
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