On Sun, 11 Nov 2001, Tony Duell wrote:
  For most makes of disk drive, you look at that label
under a
 mains-operated fluorescent lamp. There are 2 circles of bars, for 50Hz
 and 60Hz mains. Twrak the preset until the appropriate circle looks
 stationary. I can well believe the Apple Disk II uses the same
 procedure. 
That was it.  I can't remember where I read the procedure.  If it's not in
the DOS manual then I don't know where I read it.
Sellam Ismail                                        Vintage Computer Festival
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International Man of Intrigue and Danger                
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