If you are not careful you'll mis-interpet some of the scatter that makes it's way back to the transducer. These false alarms will slow you down and make you investigate closer. The edges of the rat hole will dance off the screen giving you more to look at and then you'll need to take a slower more cautious look to weed out or discipher those signals. I'm sure you know what I'm talking about, don't you? Funny how I can ask the welder to grind them up a little and smooth them out with a hole grinder and they just disappear off the scope, I guess they still call it a scope, don't they?(screen). The USN 50 we have here at work is a good little machine though, it's easy to set up and use. Calibrations are a breeze with all those data sets to plug away and recall when you need them. I honestly don't zero out the machine each time I calibrate. Just recall the data set for say, the 70 SW or 60 SW, and check it against the ref block. The USN 50 seems to never move, always dead on regardless of the power source, or low or full batteries. I bought a USN 52 for myself off ebay and thought maybe I would use it on the side for some extra change, but then we started all these long hours and I could hardly keep up here in the shop, so I ended up selling it to an inspection outfit in South Carolina.
Gotta get back out there, more columns will be ready in a little while.
John Wright