Well, Jonz got it right. I can remember my grade school teacher using one to draw circles on the black board. I have also seen David Marks use one to draw large circles on wood. I picked this up at a yard sale for $2.00. I believe it is made of maple and although I don't know for certain how old it is, I would suspect it is at least 50+ years old, maybe more. I have seen others on ebay but they don't look quite as elaborate as mine. I may never use it but some day I just might. Who knows what may lurk around the bend.