Wondrous Item, common
This faintly glowing abacus is fitted with smooth white beads. As an action, you can hold the abacus and point at a collection of objects or creatures that fit within a 5- foot cube. The abacus instantly counts out the number of items in the collection, then displays the result using its beads.
This is a great item concept. Depending on setting, the rarity of common could make sense I guess.