StretchwisePitch raises and one-string raises
When a piano is well below pitch, raising each string exactly to its target doesn't hold. As later strings come up, the extra load on the plate and soundboard pulls earlier ones back down. A pitch raise tunes each string past its target by a share of how far it had to move, so the piano settles close to pitch, ready for a fine-tuning pass.
Turning it on
Tap Tuning settings in the toolbar and switch on Pitch raise. An orange banner shows the percentages in use, with "limited" added when a cap applies. Switch it off when the raise is done to return to your final targets.
How the overpull is worked out
Stretchwise doesn't survey sample notes first. The first confirmed reading of each note becomes its start: how many cents it sits from its final target (stretch curve, temperament and any correction). The banner shows "Started −x cents · overpull +y". A start is taken only from the string you're tuning, never from the one before it that may still be ringing. If you come back to a note more than two minutes after leaving it, it's measured afresh. Use Re-measure to take a new start.
The overpull is the start times a percentage, in the opposite direction, kept within a limit. The percentage depends on the section:
| Section | Default | Limit |
|---|---|---|
| Wound strings (to the last wound string, F3 unless set for this piano) | 10% | 10 cents |
| Plain wire | 30% | 50 cents |
| Treble (F5 up) | 36% | 50 cents |
For example, a plain-wire note 20 cents flat gets a target 6 cents sharp. A treble note 12 cents sharp gets a target 4.3 cents flat. The meter reads against the overpull target, so you tune to zero as usual.
Each percentage can be set from 0 to 60%, and each limit from 0 to 100 cents. Last wound string can be set for the piano in front of you, and Restore defaults puts everything back. The default percentages follow Verituner's published defaults, and the limits follow TuneLab's worked example. Many technicians use smaller bass limits, some as little as 1 to 3 cents, so set them to suit your practice.
If you prefer two passes, switch on First of two passes (no overpull) to bring everything near pitch without overpull, then do the fine pass.
One-string raise
With Pull one string per unison on, you raise one string of each unison while the others are muted. That string is pulled further, so the unison as a whole carries the tension it will have at pitch. The banner gives the extra amount, for example "Pull 1 string of 3 a further +x cents (others muted)". For a trichord 10 cents flat, that's about 19.7 cents above the target; for a bichord, about 9.9.
The pull and the overpull together are kept within the section limit, and never above 55.9 cents. That figure comes from published wire-stress limits for piano wire. If one string would need more, Stretchwise asks you to pull two ("Too far for a safe one-string pull…"), and at most it asks you to tune every string to the target. Single-string and two-string sections are set by Last single-string note (E1 by default) and Last two-string note (C3). For single strings the banner says "Single string: tune it to the target." Stretchwise gives targets for the pulled string only, so bring the muted strings up in your usual way.
After the raise
Pitch readings aren't saved during a raise, but each note's inharmonicity is. When you switch the raise off, the fine pass starts from a stretch curve built from this piano (see how the curve is built).
Use your judgement
The percentages and limits come from published defaults, and the arithmetic is checked by automated tests against worked examples from those sources. They haven't yet been confirmed on real pianos in the field. The one-string model balances each unison's own tension, not the whole plate. It assumes the strings in a unison are identical and sound. Old, rusty or previously repaired strings need lower limits, and the call on whether a string will take a pull is always yours.