TUNIC only:pure Piano Tuner

The TUNIC only:pure is a piano tuning software for professional piano tuners and concert technicians for iPhone and iPad.
It is superior to other common piano tuning software because of:
1. No special tuning sequence is required. Select the desired pitch for A4, start at a note of your choice and tune string by string.
2. It is not necessary to pre-measure inharmonicity before actually tuning the instrument.
3. Several pianos, even with different inharmonicity profiles, can readily be tuned together. Simply select the same pitch for all pianos.

PURE TWELFTHS EQUAL TEMPERAMENT
TUNIC only:pure Piano Tuner tunes the piano using equal temperament on duodecimes (the interval that spans an octave and a fifth - also known as "Stopper tuning" or "Stopper temperament" developed by B. Stopper in 1988), resulting in a theoretical semitone step of the 19th root of three, as opposed to the twelfth root of two in pure octave tuning.
The pure twelfths equal temperament tuning method has become a new standard in the concert halls in the past 30 years, and widely been used by professional piano and concert technicians worldwide.

HARMONIC EQUIVALENTS AND EFFECTIVE PITCH
Due to the inharmonicity of piano strings, the pitch of a piano tone typically deviates from that of a corresponding harmonic tone (e.g. approx. 0.8-0.9 Hz for A4, whereby the exact value depends on the non-linearity of the strings).
TUNIC only:pure takes this effect into account by the method of "harmonic equivalents": For a given pitch (e.g. A4 at 440Hz), only:pure automatically tunes the instrument such that the best possible impression of a harmonic tone is perceived.
Please note that this means that the actual pitch of an instrument tuned with only:pure typically differs by 0.8 - 0.9 Hz from the fundamental of corresponding tone with harmonic partials.
NOTES REGARDING USAGE OF THE TUNING APP
Depending on your device, prior to the first usage, you may need to set the microphone gain once in order to achieve satisfactory results. To do so, tap on the button "PITCH/Mic Gain" while playing some keys. Increase the microphone gain (initially set to 1.0) until the indicators move smoothly and/or the note recognition works reliably.
While tuning, please ensure that your device is located as close as possible to the string that you're tuning, especially in the treble. In case the program reacts sluggish, you may also try to change a different microphone input, by tapping on the left microphone label.
The current effective pitch (see preceding section) is displayed by the number in the top left area of the screen.
Finally we note that TUNIC only:pure is primarily a tool for skilled and experienced piano tuners and concert technicians. Due to its high-responsiveness, the software may be difficult to control for beginners and part-time piano tuners.

AVAILABLE VERSIONS AND IN-APP PURCHASES
The standard version of TUNIC only:pure includes a chromatic note switching mode as well as fully automated note recognition. 
The basic variant only allows for manual note switching by tapping the buttons at the bottom of the main screen.
You have the possibility to choose between either subscriptions (on a monthly or yearly basis) or permanent purchases. To find available versions, tap on the "Shopping Cart"-Icon on the main screen.
Please note that if you choose to have subscriptions, your device requires access to the internet from time to time, in order to communicate with Apple services validating your subscriptions.
Please further note that major future developments and/or feature enhancements will only be provided to subscription customers. However, bug fixes, minor improvements as well as support for new device generations will be provided for all versions of TUNIC only:pure.
TERMS OF USE:
https://www.apple.com/legal/internet-services/itunes/dev/stdeula/