A real piano string produces upper partials that run progressively sharp of exact whole-number multiples because the string has stiffness. That physical departure, called inharmonicity, means a perfectly accurate chromatic tuner can still aim at the wrong place on an acoustic piano.
A generic chromatic tuner usually solves a simpler problem. It detects a pitch, compares it with a pre-calculated equal-tempered target, then reports how many cents sharp or flat the note is. For guitars, winds, and quick pitch checks, that can be exactly what you want.
A piano needs a different target before measurement accuracy even enters the argument. Tune every fundamental to an unstretched equal-tempered grid, and important partial relationships will not line up cleanly across the keyboard. The detector may be accurate, while its mathematical destination ignores part of what the piano actually produces.
That matters when two notes form an octave. A simple tuner expects a precise 2-to-1 relationship between their theoretical fundamentals. A piano technician also considers partial relationships, so widening an octave can bring important components of both notes into better agreement.
That creates the familiar pattern of bass notes falling below an unstretched line and treble notes rising above it. The correction is not fixed across the keyboard because different strings can carry very different amounts of inharmonicity.
This is instrument-specific octave stretch, not a correction you can copy blindly from one piano to another. Professional tuning software shows that measurements can vary substantially across one keyboard, especially near the extremes. Shorter or poorly scaled instruments can also behave unevenly around changes in stringing.
That distinction separates pitch detection from target calculation. A chromatic tuner may measure a frequency precisely yet call a useful piano target sharp or flat because its zero assumes an unstretched scale.
That makes an individual piano stretch curve more useful than simply making a chromatic display more sensitive. The meter's zero now represents a target derived from the piano's acoustic behavior rather than a generic frequency table.
Sophisticated systems can also let the technician decide which interval relationships deserve more weight. Octaves may be judged through different partial pairings, while fifths and twelfths can influence the calculated curve. No single stretch value makes every interval pure because the piano's inharmonic partials force a compromise.
A familiar Railsback-style shape is therefore a useful broad pattern, not a universal template. Real measurements can depart from a neat, smooth curve from note to note. Some software deliberately gives measured inharmonicity more weight on poorly scaled pianos, accepting a less tidy curve for closer partial alignment.
Two competent piano tuning programs can therefore suggest slightly different targets even when their detectors closely agree on the measured frequency. Different interval priorities, inharmonicity models, and smoothing choices can still change where the calculated note should finish.
Entering A4 at 440 Hz does not solve the missing stretch calculation. Concert pitch establishes a reference point, while stretch determines how targets depart from equal temperament across the keyboard. They are separate settings with different jobs.
The practical distinction is visible in what the device measures. A fixed-grid tuner compares the piano with a generic scale, while a piano ETD measures partials and recalculates instrument-specific targets.
Calculated targets still do not replace judgement at the tuning hammer. Professional systems retain aural interval checks, manual curve adjustments, and alternative stretch choices because measurements can be imperfect. False beats, weak partials, noise, and irregular scaling can all complicate what the screen reports.
Low and high registers add another practical problem because the fundamental is not always the strongest useful component of a piano tone. Piano-specific systems can track selected partials and relate them to calculated targets, instead of relying on one generic pitch reading.
A generic chromatic tuner usually solves a simpler problem. It detects a pitch, compares it with a pre-calculated equal-tempered target, then reports how many cents sharp or flat the note is. For guitars, winds, and quick pitch checks, that can be exactly what you want.
A piano needs a different target before measurement accuracy even enters the argument. Tune every fundamental to an unstretched equal-tempered grid, and important partial relationships will not line up cleanly across the keyboard. The detector may be accurate, while its mathematical destination ignores part of what the piano actually produces.
Piano inharmonicity changes the target itself
Ideal strings have partial frequencies at exact whole-number multiples of the fundamental, but piano wire is not ideal. Its stiffness pushes higher partials progressively sharp, and the amount changes with string length, thickness, tension, scale design, and position.That matters when two notes form an octave. A simple tuner expects a precise 2-to-1 relationship between their theoretical fundamentals. A piano technician also considers partial relationships, so widening an octave can bring important components of both notes into better agreement.
That creates the familiar pattern of bass notes falling below an unstretched line and treble notes rising above it. The correction is not fixed across the keyboard because different strings can carry very different amounts of inharmonicity.
This is instrument-specific octave stretch, not a correction you can copy blindly from one piano to another. Professional tuning software shows that measurements can vary substantially across one keyboard, especially near the extremes. Shorter or poorly scaled instruments can also behave unevenly around changes in stringing.
That distinction separates pitch detection from target calculation. A chromatic tuner may measure a frequency precisely yet call a useful piano target sharp or flat because its zero assumes an unstretched scale.
Piano tuning devices model partials before showing zero
Purpose-built piano tuning software takes another route. It samples partials from the instrument, estimates inharmonicity, and uses those measurements to calculate targets across the range. Different systems measure every playable note or build a model from several samples spread across the keyboard.That makes an individual piano stretch curve more useful than simply making a chromatic display more sensitive. The meter's zero now represents a target derived from the piano's acoustic behavior rather than a generic frequency table.
Sophisticated systems can also let the technician decide which interval relationships deserve more weight. Octaves may be judged through different partial pairings, while fifths and twelfths can influence the calculated curve. No single stretch value makes every interval pure because the piano's inharmonic partials force a compromise.
A familiar Railsback-style shape is therefore a useful broad pattern, not a universal template. Real measurements can depart from a neat, smooth curve from note to note. Some software deliberately gives measured inharmonicity more weight on poorly scaled pianos, accepting a less tidy curve for closer partial alignment.
Two competent piano tuning programs can therefore suggest slightly different targets even when their detectors closely agree on the measured frequency. Different interval priorities, inharmonicity models, and smoothing choices can still change where the calculated note should finish.
A chromatic tuner still has useful limits
None of this makes a normal chromatic tuner useless around a piano. It can show whether the instrument is near its reference pitch, expose a displaced note, and provide a rough survey before finer work.Entering A4 at 440 Hz does not solve the missing stretch calculation. Concert pitch establishes a reference point, while stretch determines how targets depart from equal temperament across the keyboard. They are separate settings with different jobs.
The practical distinction is visible in what the device measures. A fixed-grid tuner compares the piano with a generic scale, while a piano ETD measures partials and recalculates instrument-specific targets.
Calculated targets still do not replace judgement at the tuning hammer. Professional systems retain aural interval checks, manual curve adjustments, and alternative stretch choices because measurements can be imperfect. False beats, weak partials, noise, and irregular scaling can all complicate what the screen reports.
Low and high registers add another practical problem because the fundamental is not always the strongest useful component of a piano tone. Piano-specific systems can track selected partials and relate them to calculated targets, instead of relying on one generic pitch reading.
