Let me report what SteveW wrote:
"This object is an on-the-fly surveying device. Worn on a chain around the neck, a military officer could hold it out to arms length and "fit" an enemy soldier or catapult, ballista etc between the opposing holes and then multiply by 100 (or whatever factor/number of links of the chain) to guage his distance. It would have been accurate enough to place a man within a few feet up to roughly a mile away. "
This is a quite good reference for my paper A Roman Dodecahedron for measuring distance
A figure from my paper http://arxiv.org/abs/1204.6497
Somebody is considering that there are also dodecahedra of stones. These were tools for gambling, please see An Etruscan Dodecahedron http://arxiv.org/abs/1205.0706 or the previously written post.