I got an email from Woodpeckers this morning for this item:
I use two pieces of beaded pine screen molding and two medium bulldog clips to accomplish the same thing.
I cut the molding to an appropriate size and then turn the two pieces so that the ribs are facing each other and will mesh like gears. This keeps them in alignment and practically eliminates any slippage. For inside corners, I miter the ends for greater accuracy.
This is the molding profile:
And this is the type of clip I use to clamp the molding in place (use 2 clips).
They last until I accidentally step on one and break it. Most recently I used it to measure crown molding in just under a 12' length. First cut was right on the mark.

I use two pieces of beaded pine screen molding and two medium bulldog clips to accomplish the same thing.
I cut the molding to an appropriate size and then turn the two pieces so that the ribs are facing each other and will mesh like gears. This keeps them in alignment and practically eliminates any slippage. For inside corners, I miter the ends for greater accuracy.
This is the molding profile:
And this is the type of clip I use to clamp the molding in place (use 2 clips).

They last until I accidentally step on one and break it. Most recently I used it to measure crown molding in just under a 12' length. First cut was right on the mark.