Pocket Orchestra has two modes - Tuner and Scale Builder. This page will go into depth on both.
Scales can be loaded from file on this screen. If no .scl or .scale files are found in the scale folder, Pocket Orchestra automatically uses a 12-tone equal tempered scale. Users can temporarily edit the fundamental frequencies of their scales - this allows for quick transition between (for example) A = 438 Hz and A = 440 Hz equal temperament, without creating an entirely new scale file. Users can also specify which note should act as the fundamental. This way (for example), an F just scale and a G just scale can be stored in the same file and edited whenever it comes time to tune. Pocket Orchestra automatically calculates the standard A = 440 Hz pitch for these notes so you don't have to; however, the pitch is also fully customizable.
After the scale is loaded and the optional additional settings are specified, pressing "Set and Tune" begins the actual tuning process. The tuner uses autocorrelation hand-in-hand with a precise quadratic approximation to give results accurate at frequencies as high as 8000 Hz (to within 2 Hz). At more common frequencies, results are reported accurately to at least two decimal places. Pitch data is reported every quarter second in a minimal and color-coded display. Green text means that the pitch is approximately in tune, yellow and red mean that the pitch is going sharp or flat. The rate at which the text turns from green to red is directly proportional to how far apart the notes are spaced - everything changes dynamically to the loaded scale.
At the start of the Scale Builder wizard, users can specify whether they want to build their scale from scratch or edit an existing scale (sometimes using it as a template). Users can specify the names of notes, their relative pitch in cents, their ratio to the tonic frequency, and their absolute pitch in Hz. All the math required to convert between these data types is automatically computed by Pocket Orchestra - no calculators needed! In addition, tools to automatically set the scale to X-tone equal temperament and to sort the scale are provided. Scales save to either the .scl or .scale format - no preference. Pocket Orchestra ensures that any scale saved using the Scale Builder will be compatible with the Tuner mode.
For more information on how Pocket Orchestra works, particularly on the math of the tuner, visit the how it works page.