Originally Posted by TiredFeet
Asked TeeDee about this and he said not to get hung up trying to get the 30 degree sag angle.
But if you want, there is a very easy method for determining when you have a 30 degree sag angle.
While that is a rather precise method it requires more work than I'm will to put into it while out in the piney woods. When I first started hanging last year, I built an inclinometer that worked based on a plumb bob. I took a small piece of 1/4" plywood and used a protractor to mark out a vertex and 10 degree angle increments along the semi circle. I drilled holes at each point. I threaded a loop of string through the vertex point. To use it I attach a small carabiner to the loop and hold the reference edge with the vertex to the suspension and read the angle off the scale. It's simple, low tech, zero cost and weighs next to nothing.
Although in retrospect, I really like oldgringo's thumb and index finger method.