I took a 13' piece of the NER throwline (zing it would work great, too). I spliced an eye one one end. This is the "zero-eye" mark. Then I tied an over hand knot 3.14159 down the rope. This comes to 37 11/16ths of an inch.
I went down another 37+ inches and tied a double overhand. Went again tying a triple overhand, and one more time, tying a quadruple overhand knot.
So now I could walk up to a tree, feed the tail end through the zero-eye, then pull tight. I find the last knot. If the first overhand knot is even with the zero-eye, then the tree is exactly 1' DBH.
If it's somewhere between 2 knots, you have to estimate.
I took it a step further. I put 5 marks (tiny whippings) between each knot. They are color coded- red, orange, yellow, green, blue. The colors of the rainbow. There is one every 2" x pi. This comes to 6 1/4". Now, I can look through and estimate DBH to the nearest 2"!
In the picture above, that Liquidambar styraciflua has the orange mark at the zero-eye. That tree is about 1' 4.5" DBH.
It seriously took me about 2 hours to make the whole thing with whippings and everything, but I have a neat little tool that will take the guess work out of measuring trees
love
nick
note- I wanted a lighter weight option than carrying a measuring tape. Back-country hiking is best when you have less to carry!