The four criteria for assessing class importance apply to hengi-form monuments as follows:
- Period (currency): Long lived. The tradition of constructing and using hengi-form monuments probably continued for five centuries or more spanning most of the later Neolithic period. The sanctity of the monuments seems to have been even longer-lived as several appear to have been reused for burial in Bronze Age times.
- Rarity: Very rare. Only about 24 hengi-form monuments are known with certainty, although there may be as many as 40 or 50 recorded from aerial photographs but as yet not authenticated.
- Diversity (form): Medium. Three main types of hengi-form monument can be identified on the basis of currently available evidence.
- Period (representativity): High. Hengi-form monuments represent one of a fairly restricted range of monuments known from the later Neolithic period. It may be noted, however, that they probably represent one of several broadly contemporary classes of monument closely associated with ritual and ceremonial activities.
Assigning scores to these criteria following the system set out in the Monument Evaluation Manual, hengi-form monuments yield a Class Importance Value of 45. This lies over two-thirds of the way up the range of possible values (max.= 64) reflecting rarity and longevity of the class. Examples representing the full range of types, and variations in size and orientation, must also be included in the sample of nationally important sites. It may be noted, however, that many of the known sites no longer exist because they were discovered and excavated just prior to or in the course of their destruction. This makes the sites that do remain all the more important.