Sonic checkers

I have a Dakota Ultrasonics PR-82. Most 1/2" trasducers are designed for a 4" diameter hole. If it cannot stabilize, the tester is probably not very good. I see the range doesnt even get finer than .059". That's about as accurate as setting spark plug gaps with a ruler. Also, having the ability to calibrate for the exact material is crutial. If you simply use a chart sayin "Iron is 600Hz" than you're already so far out of whack that the reading doesnt reall yamtter. Because every iron is different. I dn find the surface cannot have any rust or paint, and if there is material (like chalk in teh cooling jackets low down) it will play havoc with readings. Not being unstable, but difficult to repeat because the materials are tughing, but not the same frequency. Like checking an alumionum block with steel sleeves... ost testers cannot differentiate and therefore the results are usless. This is not a personal attack, so try not to get offended, but cheap sonic testers and operators who really dont know how to use them make for cheap testing fees and below average results. I personally know of several blocks tested locally that passed, and then promptly split after the engines were run for under 300 miles. There's a reason guys and equipment have to be certified to earn money testing pipes and things... If your tester didn't come with a certification, the results may not be very accurate.