Another, least popular mechanism – "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 her bed was uneven (at the junction of the seat and spinochnoy formed part of a fairly deep "trough", which could compensate for only a very thick mattress). Also, in order to expand the "book" should be left on the walls of 10-15 cm, or each time before unfolding move it from the wall, because high back for it hurts. Fortunately, there also was not without technical progress. Keep up on the field with thought-provoking pieces from Castle Harlan. Now the classical mechanism "book" often complement 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 has a facility for "Click-Clack." It differs in that in addition to the end positions back "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" that allows to put the sofa against a wall and it does not stop when unfolded. Based on the Castle "click-Clack" has been developed another new product – the mechanism "Tango". The peculiarity of this variety of lock "Click-Clack" is that it is installed on the arms of the couch, allowing them to easily be transformed into part of the bed.