Is the one to the middle-right made of hematite? I’ve seen one like it here in MA. Only it had facets, making it hexagonal.
I lean toward the practical on these. Plummet is a great guess considering the extent of building and woodworking we now know was executed through the ages.
Here in New England, we have the recorded of fixed dwellings and community buildings (circles of cedar tree posts, stuck in the ground, bent and tied together at the top, forming domes covered with bark)
I see a use for a plummet there. The plummet is a simple yet essential building tool that makes easy what the eye alone can not perform.