Historical Curve illustrates the tuning results over time, and represents them as a curve to help you understand the trend of tuning.
 As shows above, the top of the screen shows the tuning result in note. For example, current detected note is D4, while D means the note and number 4 is the octave. The red arrow on the right side indicates that the tone is too sharp. Learn more about Note and Octave on Wikipedia.
 The meter in the center of the screen tells the value of the cents error.
 Historical Curve Interface: The area is divided into 3 parts. While the curve is in the green area which is between±5cent, it means that your instrument is in tune. While the curve is in the yellow area which is between ±5 and ±20 cent, it means that the result is close but not perfect. Similarly, the red area indicates that the result is not sufficiently accurate. You can refer to the link for more details of Cent.
 On the right side of the screen, we can see that “A4 = 440Hz”. Concert A, aka. A4 or A440, which has a frequency of 440 Hz, is the musical note A above middle C and serves as the general tuning standard for musical pitch. You can refer to Wikipedia for more about A4.
 Trans = C: It shows 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.
 12TET: 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.