The following image shows the interface of Fine-Tuning Unit. The top-to-left note shows the current detected note. Its color varies depending on the degree of its accuracy.
 Current Detected Frequency: Frequency is another measurement of note. While higher frequency represents higher note, lower one represents lower note. Take the previous figure for example, current detected frequency is 220.2 Hz.
 Current Detected Cent：The cent is a logarithmic unit of measure used for musical intervals. Twelve-tone equal temperament divides the octave into 12 semitones (C,C#,D,Eb,E,F,F#,G,Ab,A,Bb,B) of 100 cents each. Typically, cents are used to measure extremely small finite intervals, or to compare the size of comparable intervals in different tuning systems, and in fact the interval of one cent is too small to be heard between successive notes.
The “+10.2 cent” showed in the image tells us that the difference between the detected frequency and C0 is 10.2 cent, while the “+” represents the result frequency is higher than C0. More details of Cent on Wikipedia.
 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.
 Needle: The needle shows the difference (in cent) between the detected frequency and the theoretically in tune frequency. The range of the meter is ±30 cent.
When the error is over ±10 cents, the note will turn in red, which means it is not sufficiently accurate. The note will turn in yellow until the error is between ±5 cents and ±10 cents, which is close but not perfect. When the note turns in green, the result is within ±5 cents. As human ear cannot distinguish a difference in pitch of 5-6 cents, your instrument is in tune now.
You can still try to tune to optimize the tuning result till perfect.
 Concert A, aka. A4 or A440: 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.
 Current Temperament Settings: 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 to a logarithmic scale. It is usually tuned based on the standard pitch of 440 Hz, called A440. Refer to the following link for more about Musical Temperament.
* Tips: You can pull down the top area to find all available Tuning Units, and switch between them quickly.