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In the latest issue of the Webb Society "Deep Sky Observer", Ron Morales
proposes a basic scale of averted vision in an attempt to quantify what we
mean by averted vision. I don't how many of us would want to use this type
of technical scale on a regular baseis, but keeping these concepts in mind
when you take notes would be very helpful in comparing observations.
AV 1: The object is seen with averted vision, but once found could be seen
occasionally with direct vision.
AV 2: The object is seen only with averted vision but is held steadily.
AV 3: The object is seen with averted vision only occasionally as it "comes
and goes with the seeing conditions. In this case the object is seen more
than 50% of the time.
AV 4: Again, the object is seen with averted vision only occasionally as it
comes and goes with the seeing condition, but in this case is seen less than
50% of the time.
AV 5: The object is only glimpsed with averted vision after continuously
viewing the field for a few minutes or more. This level of averted vision
occurs when one observes a field carefully for a lengthy period of time. My
notes indicate that this often occurs within the first three to five minutes
of viewing the field.
