Another thanks to Jim. He was nice enough to loan me his TDR for a couple of months, to try it out. I have to say it worked quite well for me. This is how I got started. I measured the distance to some known valves and using those numbers, I reset the VOP to 18%. This gave me real close numbers for the distance of some known valves. I took it on a service call. I was told that four valves in the front didn't work; Two valves in the back did. Hooked the TDR to one of the zones in the front. It gave me a length of 10 ft. (1st photo) While I was at the controller I decided to see how close the two good valves were; the readings were 66 and 68 and the actual distances were 33 ft and 34 ft. respectively (photos 2 and 3) They were right on. Turns out the two valves in the back had been rewired at one point, so I had two wire paths. The 10ft length was under concrete, next to a huge tree. I found the common on the second wire path (to the valves that are in the front). I ran a line to the two good valves in the back. Everything works now. My total time couldn't have been more than an hour and 15 min. Used it on the second call. Two valves not working. Different locations in the yard. Hooked the TDR up to one zone wire; said it was 20ft away. Hooked the TDR to the second zone wire; said it was 20 ft away. Hooked the 521 up, went 20 ft and this is what I found. (photo 4) The installation of the termite bait had cut the two wires to the front yard. This one also had two wire paths, the back yard was added after the front. I think the TDR is going to be a great tool in combination with my other resources. It might even make it to the front of the line.