Hornung, one of the leading wizards in the field of wild magic (before his untimely disappearance while experimenting with wildwind ), developed this spell to improve the accuracy of his estimates. The spell provides a wizard with an instant and highly accurate estimate of the number of persons or objects in a group.
The spell's area of effect is one group of a general class of objects. All objects of the group must be within spell range and the group as a whole must be visible to the caster. The wizard need not see every individual in the group, merely the general limits of the group's size and area. For example, a wizard on a hill could look down on a forest and estimate the number of trees in all or part of it. He could not get an estimate of the number of goblins within the forest, however, since the group as a whole (the goblins) is concealed from sight.
The estimate generated is accurate to the largest factor of ten (rounded up). For example, if Hornung's guess were cast on a group of 439 horsemen, the estimate would be 400. If there were 2,670 horsemen, the spell would estimate 3,000. If there were 37 horsemen, the answer would be 40. Clearly, using the spell on small groups (especially those with fewer than 10 members) is pointless.
Hornung's guess can be used to quickly estimate the size of treasure hoards and army units. It is particularly popular with moneylenders and generals.