Stretch tunes the piano in front of you, not a table of numbers. Play a handful of notes and it reads the partials of each string, fits that instrument's inharmonicity curve and calculates a target for all 88 keys. The microphone, the mathematics and your client files all stay on your iPhone or iPad.
MEASURE
• Play five notes and Stretch hears every partial, note by note
• Inharmonicity coefficients are fitted per piano, from the bass to the top octave
• A confidence reading and an input level meter tell you when a note has really been heard
• The curve is saved with the piano, so the next visit starts where the last one ended
TUNE
• A strobe that drifts left when flat, right when sharp, and freezes when the string is right
• Cents, partial number and a note name large enough to read from the music desk
• Auto-advance follows you up the keyboard; manual select keeps you on one note
• An 88-key progress strip shows what is done and what is left
• Unison helper with a beat-rate display
STRETCH AND TEMPERAMENT
• Octave widths from 2:1 through 4:2 and 6:3, blended, with separate bass and treble stretch
• Equal temperament and the historical ones: Werckmeister III, Kirnberger III, Vallotti, Young, meantone and more
• A4 reference anywhere between 392 and 466 Hz
PITCH RAISE
• Measure the starting pitch section by section, compute the overpull, tune in two passes
• A warning before a raise large enough to need care
CLIENT FILES
• One file per piano: client, make, model, serial, location, notes and the measured curve
• A due-for-tuning list, so the next call is obvious
• A before and after deviation chart across all 88 keys, exported as a PDF the client keeps
• Synced through your own iCloud with CloudKit — no account, and no server of ours
Home mode is for owners and students: check how far the piano has drifted, touch up unisons between C3 and C6, and get a plain warning when a job needs a technician rather than an app.
Stretch is free to check a piano and touch it up with. Home Plus is a one-time purchase that opens all 88 keys, the unison helper and the historical temperaments. Pro — measured stretch, pitch raise, client files, PDF reports and the Apple Watch display — is a one-time unlock you keep, or an annual subscription with a 14-day free trial.
