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Manual approach
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Automated approach with Alisa
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The visual procedure is extremely slow, tedious and prone to operator error.
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Very easy to use: quick alignment using the precise indications (direction and magnitude) given by the software.
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Visual centering is affected by subjective bias which varies from one operator to another. Even for the same operator, it varies from one day to another.
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Centring is done by software, and is objective. The errors of the centroids are known.
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A hand written record is generally kept. Obtaining graphs is time consuming.
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The values are stored on the PC. Graphs are obtained on-line. They can be stored for later reference.
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Air turbulence can affect the visual estimates.
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The effects of air-turbulence can be minimized by integrating many CCD frames.
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Monitoring the stability of the any structure is difficult after the alignment is over.
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The telescope and the CCD can be left mounted on the structure after the alignment for monitoring its stability.
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It is very
difficult and tedious to achieve a precision of better than 5 µ in the centering.
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It is possible to achieve a precision of better than 5 µ with the automated system, with no extra effort.
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