As shows on the Advanced page:
 Tuning Units: You can switch between different Tuning Modes by change the Tuning Units here. We’ve supported Historical Curve, FFT, and 4 more Tuning Units. The function is just the same as pull down the Tuning Unit (Chapter 3, Tips)
 A4 Calibration：Concert A, aka. A4 or A440, which has a frequency of 440 Hz, is the musical note A above middle C and serves as a general tuning standard for musical pitch. You can refer to Wikipedia for more about A4.
In the detail page of the A4 Calibration, you’re allowed to input the frequency directly by keyboard . You can select a specific frequency  or input the frequency by detecting the reference sound. After tapping “Detect”, it will change into detecting mode to detect the frequency you’ve played (380Hz-480Hz) by microphone. The accuracy of A4 calibration is 0.1Hz.
 Musical Temperament and Historical Temperament
In musical tuning, a temperament is a system of tuning which slightly compromises the pure intervals of just intonation in order to meet other requirements of the system. Most instruments in modern Western music are tuned in the equal temperament system.
The most common tuning system is 12 Tone Equal Temperament, aka. 12TET, which divides the octave into 12 parts, all of which are equal on a logarithmic scale. It is usually tuned based on the standard pitch of 440 Hz, called A440.
Once after tapping the Temperament option, you’ll see the Temperament Setting page. We provide many useful historical temperaments including Bach and Just etc. You can also customize your own temperament by tapping Edit on the top right of the screen.
 Transposition: It show the Current Transposition. The transposition function is very useful for transposing instruments like French Horn (F Key) and Saxophone (Bb Key). The default key without transposition is set to C.
 Notation: insTuner supports different ways of display the notes, including English (CDEFGAB), Solfège (DoReMiFaSoLaSi) or even Indian Notation (SRGMPDN). Switch between notations will affect the note display (as  in Chapter 3)
 Needle Damping: Select from Low, Median and High damper will make insTuner respond pitches differently. If the damper is set higher, insTuner will respond pitch more slowly.
Low damper will be suitable for pulse while Median damper will be great for plucked string instrument. The High damper is highly recommended when tuning Violin, Viola and other bowed string instruments.
 Tone Generator：insTuner also features a Tone Generator just like a pitch pipe with four different wave forms: Sine, Square, Triangle and Saw tooth. Each tone is optimized for different scenario. For example, as iPhone’s microphone cannot generate too low waveforms, you’ll not hear the tone when selecting Sine waveform. However, Square waveform will works fine on this situation.
 Input Channel：insTuner supports to switch inputs between different microphones. As we know, iPhone has 3 separated microphones， and insTuner makes it possible to choose one specific microphone to detect tones. (Bottom microphone is used by default)
Moreover, insTuner supports other input devices as Apogee One, etc. This will make your tuning even more accurate.