So far I have not broken a plate but have found that there are tell
tale warnings.  I have heard several technicians complain about strobe
tuners but they give you a warning of eminent danger.

First, I tune using the circle of fifths, tensioning the frame equally
rather than just tuning the mid section.  I was tuning a Steinway
Duo-Art upright and mid-way through the tuning noticed that a number
of notes unexplainably were going sharp on their own!  I also noticed
the overtones (octaves depicted on the tuning wheel) were changing.
None of this could have been detected if you were tuning strictly by
ear.

I decided to investigate and pulled off the thin wood cover board over
the pin block and cast iron frame.  Much to my surprise I discovered
an eighth-inch gap had opened between the plate and the pinblock!
I quickly let the tension down on the strings.  Next, I removed the
plate bolts, drilled them through the pin block and out through the
back and then installed bolts with lock nuts which I countersunk at the
back side.  I then retuned the piano without any problems.

Did anyone ever check the plate contact to the pinblock/frame of the
piano, as sometimes this area is covered and there could be an accident
waiting to happen...

Greg Filardo