one rubber mute

[Horace Greeley]

While I do not know the genesis of the technique, it was the one in use at 
Steinway Hall in London for generations of tuners.  At least up through the 
late 1970s there were technicians there using it...some of them quite well 
known at the time, including the fellow who tuned for Gerald Moore (among 
many, many others) for several decades.

It is not my preferred technique, to be sure.  However, it is like so many 
other things, a tool to have in your kit, to be used as necessary and 
appropriate...to be thought of as an expansion of one's abilities, not a 
millstone to be quickly discarded.

Best.

Horace