Depending on the manufacturer and model of such a mechanism can be equipped with rollers to facilitate sliding block of seats on the guide and the rear backrest, which will protect you from contact with the cold wall. Typically, the model with the mechanism of "" have a spacious linen compartment, which is especially valuable in cramped housing conditions. Another very popular mechanism – the "book". Previously, it was probably the only commercially available mechanism is not without drawbacks, however. The main disadvantage of "books" was that due to peculiarities of production in the unfolded form of her bed was uneven (at the junction of the seat and spinochnoy formed part of a fairly deep "trough", which could compensate for only quite thick mattress). Also, in order to expand the "book", it was necessary to keep away from the wall 10-15 cm, or each time before unfolding to move it from the wall, because high back for it hurts.
Fortunately, there also was not without technological progress. Now the classical mechanism "book" is often complementary to the rollers on the legs that allows it to move across the floor without prejudice to the latter. On the basis of this mechanism with the development of technology appeared mechanism of "click-Clack." It differs in that in addition to the back end position "sitting" and "lying" can take the intermediate position-"half-sitting" and "recline." Different manufacturers of the mechanism of the provisions of the backrest varies from 3 to 5. There are models, which in addition to the mechanism of "click-Clack" also contain an additional mechanism for "automatic rollback of the Wall," which allows to put the sofa against a wall and it does not stop when unfolded.