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Sorry more questions on this - it's not making sense to me

Here are the debug readings with UV_Transmission set at 100 in the debug code (no cover, mounted flat) from approximately 10.00 to 10.15 today. Below is the expected solar graph which says that I should expect between 5 and 6 at this time.

I assume that the debug output avg UV is an average millivolt output of the sensor over the period? If that is the case this lines up nicely with my expected UV of 5 to 6 when you look at the output graph for the UVM30A sensor.

Unfortunately the Indice UV value does not agree - as per my original observation it is very high

Sending ID4...
ACD0 - SolarRad :428   SolarRad :585
ADC1 - avg UV   : 699  Indice UV : 8.2
 
Sending ID4...
ACD0 - SolarRad :428   SolarRad :585
ADC1 - avg UV   : 690  Indice UV : 8.1
 
Sending ID4...
ACD0 - SolarRad :427   SolarRad :584
ADC1 - avg UV   : 715  Indice UV : 8.4
 
Sending ID4...
ACD0 - SolarRad :427   SolarRad :584
ADC1 - avg UV   : 725  Indice UV : 8.5
 
Sending ID4...
ACD0 - SolarRad :427   SolarRad :584
ADC1 - avg UV   : 707  Indice UV : 8.3
 
Sending ID4...
ACD0 - SolarRad :427   SolarRad :584
ADC1 - avg UV   : 730  Indice UV : 8.6
 
Sending ID4...
ACD0 - SolarRad :437   SolarRad :598
ADC1 - avg UV   : 673  Indice UV : 7.9
 
Sending ID4...
ACD0 - SolarRad :446   SolarRad :610
ADC1 - avg UV   : 700  Indice UV : 8.2
 
Sending ID4...
ACD0 - SolarRad :454   SolarRad :621
ADC1 - avg UV   : 768  Indice UV : 9.0

Would you be kind enough to explain the mathematics behind your calculation of the UV?