Seeing in arc-sec.

Rating

Description

V  < 0.4"

Excellent 5/5

Perfect motionless diffraction pattern.

IV ~ 0.4-0.9"

Good 4/5

Light undulations across diffraction rings.

III  ~ 1.0-2.0"

Average 3/5

Central disc deformations. Broken diffraction rings.

II  ~ 3.0-4."

Poor 2/5

Important eddy streams in the central disc. Missing or partly missing diffraction rings.

I    > 4"

Bad 1/5

Boiling image without any sign of diffraction pattern.