1 – Very Poor.
Star image 2x the diameter of the 3rd diffraction ring – Star image 13″ in diameter.
2 – Very Poor.
Star image occasionally 2x the diameter of the 3rd ring.
3 – Poor to Very Poor.
Star image about the same diameter as the 3rd ring (6.7″) and brighter at the centre.
4 – Poor.
Airy disk often visible. Arcs of diffraction rings sometimes seen.
5 – Fair.
Airy disk always visible. Arcs frequently seen.
6 – Fair to Good.
Airy disk always visible. Short arcs constantly seen.
7 – Good.
Disk sometimes sharply defined. Diffraction rings seen as long arcs or complete circles.
8 – Good to Excellent.
Disk always sharply defined. Rings seen as long arcs/complete circles, always in motion.
9 – Excellent.
Inner diffraction ring stationary. Outer rings occasionally stationary.
10 – Excellent/Perfect.
The complete diffraction pattern is stationary.