maybe he has perfect pitch. you never know. however, i do believe that the tone and quality of the tone at the end of the stringjob is vital to the liveliness and playabilty of the stringbed. if at the end of the stringjob, tap the racket, if the result tone is a long and resonate nicely, the stringjob is usually lively. if it is thud that dies down quickly, the stringjob is not very lively. and i say usually as i have had cases where that isn't the case. === and this also brings up the point, there are different ways to grade the quality of a stringjob, most people will grade it by "tangible" things like how good the knots are, what pattern, cross over. but to me that's only the surface of it. the real quality is how lively the stringbed is and it is not something that one can see from inspection alone. you need to hit with the string to actually feel how well it plays.