The Leica M6 TTL is a 35mm rangefinder mechanical camera. It has been introduced after the Leica M6. Three sizes of viewfinder are available: first 0,72x and 0,85x. Later in 2000, a 0,58x model introduced.
It has TTL measuring capacity, which can be used with SCA-3000 compatible external flash (like the Leica SF20). Because of this electronic addition, the M6 TTL top plate is higher by 2,5 mm than its predecessor.
The shutter dial is also slightly bigger than before, and its direction reversed, breaking an old Leica tradition. The design was meant to keep consistency with the cell arrow's direction.
Even though the Leica M6 TTL embeds some electronics, it can still be used without battery (with rules like Sunny16). The camera will only lose the benefit from the cell.