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Remember that most indicators count up when pressed in and count backwards when extending out. So if the reading at 90 degrees was 0.017 and the 270-degree reading was 0.077, that means the bellhousing needs to be moved to the center of these two readings. The math goes like this: first, 0.077 is 0.023 away from 0.000, and since it's "less than" 0.000, in this case we need to add that amount to 0.017 to find its center (0.017 + 0.023 = 0.040/2 = 0.020). The bellhousing must be moved 0.003 inch so that the 90-degree reading indicates our new figure, 0.020 and the 270-degree reading would indicate 0.080, or 0.020 away from 0.000. After you've done this several times for both the horizontal and vertical axes, you can re-zero the indicator at the top, and it should read very close to 0.000 the whole way around.