ZENIT 12
Zenit 12, bought by Christophe on leboncoin.fr in may 2009.
The former owner of this camera had received it as a gift for her communion. It was very well maintained, the last time I saw a Helios 44M-4 so clean, it was a new one!
The Zenit 12 is an intermediary between the TTL and 12xp. It is unusual, because produced in a smaller quantity.The TTL uses a single sensor at the front of the pentaprism, with a metering by galvanometer. The 12 uses the new shell (wider at the mirror place), and two sensors on either side of the sight. For 12xp, the galvanometer will be replaced by a LED display.
Initially, the Zenit TTL and 12 used a 1.35v mercury PX13 battery; this battery no longer exists, it has been replaced by the 1.5V PX625 (alkaline). The light metering does not depend on the battery voltage, because the galvanometer's needle indicates a correct exposure when there is zero volt (metering method called "by electrical zero").
I do not know why some Zenit have a reminder frame on the back, like this one, while others (like my TTL and my 12xp) do not.