Вот специально слазил в рульбук, покопался и нашел это на стр. 6:
Bases and Base Contact
All models are placed on a square, rectangular or round base. The extent of the model is considered to be its base. Base
sizes are given as two measurements in millimetres: front‐width x side‐length.(For example,the normal cavalry base is
25x50mm). In some rare cases models have round bases. In these cases, only as single measurement is given: the
diameter of the base. (For example, a standard War Machine base is a round 60mm base).
P.S. Не благодари! :)