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I remember only a handful of nights in Oz with so called perfect seeing. Usually if it's real good you look up naked eye and you can tell straight away. No need to measure anything. It's quite obvious. Stars are just 'hanging' there. The view through a finder will be dead still. Again very obvious. Your guiding will flat line. As far as FWHM I get different readings using different programs so I don't know what to believe anymore but the best I got was around 1.5. The difference between 1.5 and 2 or 2.5 which is more the norm is quite dramatic. Realistically I get between 2 and 3 most nights, sometime 4-5 if the jetstream is out there. In the Pyrenees mountains in summer, over 1000m, on an good night the sky is very still. More than anywhere I've seen in Australia. The best I've seen would have been at 3000m in Winter. It's a bit like staring at a window in space. Nothing moves. But at -25c it would be a serious commitment.
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