The truth about accutuners is simple, but two-fold: 1) accu-tuners which measure "FAC" and calculate a tuning, will produce a tuning which often needs aural touch-up. So there's your 95%. But the final tuning can be entered into the computer for future re-use - which is highly accurate. 2) the PTG tuning exam is done by a group of RPT's tuning the piano aurally first. That becomes the "master tuning" for the piano. This "master tuning" is entered (recorded) into the accu-tuner. The piano is de-tuned a specific way. The person being tested tunes the piano, and his tuning is compared with the pre-recorded "master tuning". This comparison is also highly accurate. To sum up, the accuracy of the SAT as a frequency measurement device is higher than the accuracy of the tunings which are calculated by an FAC operation. This is because the FAC uses the stretch of only 3 notes in the calculation and cannot consider imperfections in the scaling of the piano. Dan Litwin - jerk tuning - user of accu-tuner and aural tuning techniques. San Diego Chapter PTG associate
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