The heart of a TuneLab tuning curve is the template that is made to fit a wide variety of pianos through the adjustment of four separate parameters. These adjustments can be made so that octaves or double octaves are beatless at both ends of the scale, and if you want a slight beat, you can customize the tuning curve to produce any desired beat rate in these intervals.
First, TuneLab listens to a few notes to measure their inharmonicity. You can use as many or as few notes as you like, so long as at least four notes are measured. Each measurement automatically registers as many partials as TuneLab can hear and all of them are used to calculate the inharmonicity constant for the note. Repeated measurements of the same note are automatically averaged by TuneLab. Then TuneLab takes whatever inharmonicities were measured and calculates the inharmonicity for all 88 notes - even for the notes that TuneLab did not listen to. Of course, the more notes that you let TuneLab listen to, the better this calculation will match the actual pattern of inharmonicities in the piano.
Armed with the total inharmonicity picture, TuneLab is able to display a curve that shows how wide each interval is. Both the bass and the treble section of the deviation curve may be set up to display from a long list of intervals. You may select different intervals for the bass and the treble. Select the intervals that are important to your tuning and see exactly how far each interval is from being beatless. This deviation curve is shown just below the tuning curve. For total control of the tuning curve, you can select the fully manual mode of tuning curve adjustment. To save some time and effort, you can also select the semi-automatic adjustment mode where two of the four tuning curve parameters are adjusted for you by TuneLab. And for the ultimate in time savings, you can select the fully automatic mode where all four parameters are adjusted for you based on your selection of bass and treble intervals.
The template portion of the tuning curve which you graphically adjust (or is adjusted automatically) is only one component in the total tuning curve. There is also an optional table of custom stretch offsets that you can alter separately for each note. And if you have applied an historical temperament, it becomes another component of the total tuning curve. These components are maintained separately in the tuning file so that they can be independently adjusted or removed at some later time if desired. Finally, there is an optional comment file that is associated with the tuning file by having the same name as the tuning file (except that it is a .TXT file). This file can be used to store comments about the tuning, such as repairs that may be needed in the future, or what to expect the next time you are tuning this piano