Offset: Temperature Coefficient total in PGA using AD797 and ADG412

Hi all:

Do anyone know how the calculation of the total temperature coefficient show in "Analog Device" literature of PGA, using AD797 and ADG412, increases from 0.6uV/ºC to 1.6uV/ºC? There is a 1uV/ºC part, not belonging to the AD797B, I am not able to work out. Any help is appreciated

Thank you