Metering is via the Sensor only and a Sandwiched cover glass is used.
Noise levels are affected dramatically by sensor temperature. In rangefinder mode, the sensor must be active just to provide metering. Sandwiched cover glass is a technique used to combine a glass with properties affected by humidity with a protective glass used to shield the bottom layer from humidity. Such as using S8612 with a BS7 cover. Maybe Leica has a different reason, we'll know in a few years if the bottom layer starts corroding like on the M9.
Noise levels are affected dramatically by sensor temperature. In rangefinder mode, the sensor must be active just to provide metering. Sandwiched cover glass is a technique used to combine a glass with properties affected by humidity with a protective glass used to shield the bottom layer from humidity. Such as using S8612 with a BS7 cover. Maybe Leica has a different reason, we'll know in a few years if the bottom layer starts corroding like on the M9.