Unless one is preparing to enter into something like a statistical analysis, I don't think their is much point of measuring perforations on glass beads.

When Mark measures the perforation of an agate bead, he's doing this as a significant part of studying the manner and type of drilling. He uses a caliper, like a slide rule, that has tiny prongs that can be inserted into some beads and measure aperture diameter.

The casting of the perforation channel (in dental silicon) is done to see the details of the drilling—the actual marks of the drill bit on the walls of perforations. These casts are viewed with the help of a Scanning Electron Microscope.

For our purposes, ands particularly with glass beads, the object is merely to determine whether the perforation has parallel or converging sides (is straight or tapered), and of course helpful stuff like whether their is separating compound, mandrel flaking, or nothing in the perforation.

Since Venetians didn't make beads with tapered perforations, while many Islamic Period beads do have them, and since your bead has one..., it stands to reason it is not a Venetian bead.

Jamey