Axis of the Level Tube is Perpendicular to the Vertical axis |
Test After setting and leveling the level, turn the telescope through 180 ° about its vertical axis. If the bubble remains central, the axis of the level tube is perpendicular to the Vertical axis. Otherwise, a displacement of the bubble from the central position indicates that the tube is not in adjustment. The amount of displacement is double the amount of error, by the principle of reversion (Figure 12.3).
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