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.