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Two filter wheels (A and B) are available for the calibration lamps. AFARC n and BFARC m put in position n and m the filters in wheels A and B; n and m are numbers between 0 and 7 corresponding to

Wheels A and B are used together in any combination, giving a density range
between clear and 5.10. By specifying ND * x* the software will choose
the combination of A and B equal or greater than * x*.

Wed Apr 6 22:56:39 BST 1994