On this screen you can select the bass and treble intervals that are used to determine the stretch in the Tuning Curve in automatic adjustment mode, and to draw the Deviation Curve (the lower graph on the Tuning Curve Adjuster page).  Each interval is specified by two numbers that give the coincident partials of that interval.  For example, the 4:2 octave is so-named because it is the comparison of the 4th partial of the lower note with the 2nd partial of the upper note.  For whatever interval you select, the Deviation Curve shows how that interval will turn out in the current tuning.  See the User's Manual on our support web site for more information on the role of Deviation Curve intervals in adjusting the tuning curve.  For example, adjusting to the following intervals is likely to give the following results:

 6:3 in the bass: low to moderate bass stretch

 8:4 in the bass: higher bass stretch

 4:1 in the treble: moderate treble stretch

 4:2 in the treble: higher treble stretch

 2:1 in the treble: low treble stretch

 You can also make any interval selection become the default interval selection for new tuning files by tapping on the "Make Default" button.