Pickering Seeing Scale
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.