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The focus commands are used for testing. If the head NVS parameter "vb" is set
to 1 then the focus diagnostic streaming to the monitor is enabled provided the
current focus mode is one of the plotting modes and focus is on. One set of
numbers should appear for each rotation of the drum. If these numbers do not
appear the focus is either not working or in the wrong mode. The first of the
four diagnostic numbers is the focus figure of merit with smaller numbers
indicating better performance. These should be less than 100 once the focus
has been learned. The second number is the largest focus error on the previous
rotation (in units of 1/3 micron). The third is the position in the table of
the largest error and the fourth number is the number of entries in the table.
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