Oximeter Accuracy

Hi,

I am studying the TI Oximeter solution from the reference design project POX_CCS_v2 by using AFE4400& MSP430 series CPU. From the code I can find the calculation of heart rate and SpO2. But I don't understand that when either the RED Light intensity or InfraRED intensity is different on two device, their ratio is different with the same SpO2. How does the application adjust this difference to make the answer same ? Is there any auto adjustment or calibration before calculation form the data reveived from AFE4400 ?

thanks & regards

AlphaSoft