Shows the tune of the selected mode, just like a guitar tuner. The hand indicates the 'exact' tune in cent (100 cent are 1 half tone).
The so called "Bolt-area" indicates a accumulation of good room ratios. If the red cross lies within this area you have a good chance of more evenly distributed modes.
Bolt R.H.: "Spatial Resonance and Standing Wave Patterns in Small Models of Various Shapes", JASA 10 (1939)
Bolt R.H.: "Frequency Distribution of Eigentones in a Three-Dimensional Continuum", JASA 10 (1939)
Bolt R.H.: "Normal Modes of Vibration in Room Acoustics: Angular Distribution Theory", JASA 11 (1939)
Bolt R.H.: "Angular Distribution of Normal Modes", JASA 11 (1939)
Bonello (modes per third):
Shows the number of modes per third up to your chosen limit-frequency, beginning with the lowest mode. According to the "Bonello-criteria" this function should be strictly increasing to reach a good distribution of modes.
Bonello, Oscar J.: "A New Criterion for the Distribution of Normal Room Modes" - AES-Journal(USA) 29 (1981)\n\n\
Bonello, Oscar J.: "Acoustical evaluation and control of normal room modes" - JASA 66 (1979)