What do the ring classes mean?
Class 1 Very distinct growth ring boundaries which can be followed around the trunk, even where the rings become narrow. These likely constitute true annual growth rings.
Class 2 The growth zones can be easily seen and are in most cases developed around the trunk. Rings often become locally narrower and sometimes slight intra-annual variations in growth occur, which are, however, easily distinguishable from the class 1 rings which can be clearly identified. Class 2 growth zones can be counted accurately.
Classes 2-3 The growth zones are distinct on one part of the trunk. They are often difficult to follow around the entire circumference. In most cases they probably constitute annual growth rings, less often aperiodic variations in width or false rings which can not be distinguished from true annual growth rings. The age of the stem can probably be estimated to within a few years.
Class 3 The growth zones are more or less distinct; only a few can be followed around the stem. Counts made on two different radii only seldom give the same number of growth zones. Thus, the age of the stem can only be estimated extremely roughly.
Classes 3-4 The growth zones are mostly indistinct. In a few cases the not well delimited bands go around the circumference. Aging is impossible.
Class 4 A number of more or less clear variations in growth occur. However, these rarely go entirely around the trunk. The age of the stems cannot be determined.
Class 5 There are almost no variations in growth. The age of the stems cannot be determined.
Sourced from Schweingruber, F.H, (1992), Annual growth rings and growth zones in woody plants in Southern Australia, IAWA Bulletin, 13 (4), 359 - 379