Actually, I think I learned it in HS drafting class - you know....back when one DIDN"T use AutoCad to draw things ;)

We used it to divide the drawing area into sections, using our engineering scale for the measuring device.

I just extrapolated it to a wall.....when trying to hang a three piece painting for the first time.

>That's pretty cool. I could see a triangle tool with a yard stick and sliding 90 degree bar (per Dragan's suggestion) that could be used for making accurate marks. I'll have to give this some thought. I would still have to do math, but it would be simpler because it creates whole numbers for the division. I've done a lot of carpentry and never heard of that one. Where did you pick it up?