Thanks, folks!
Nathan, I used it to make a mark at 60 degrees both ways from a straight edge, then laid it down and looked to see if the two lines (which should be 60 degrees apart) lined up with the sides of the square.
I also checked the 120 degree side against a hexagonal box I have. Everything was within a pencil-line thickness are 4 inches from the vertex, which is good enough for the work I'll be doing.
Dave, I bought a 8/4 x 8 x 6 foot board of sapele at the local lumber yard for far too much a couple years back. I've been taking small pieces off it (sometimes quarter sawn, sometimes rift-sawn) for tools for a couple years now. It's good looking stuff.