This paper introduces the synchronous manufacturing philosophy (douki seisan) devised by Nissan, and relates it to “Just in Sequence”, a common technique in current automotive industry. Literature is full of case studies, and the advantages and drawbacks of JIS have been reported. However, no attempt to model the necessary relations to make this system work has been found. In this paper, the necessary conditions concerning the lead times and cycle times of the different activities are deduced, and even the moment when they should take place. They allow us to define a strongly synchronous system. For practitioners, each condition shows opportunities for process improvement. For researchers, lack of compliance with such conditions, gives rise to maximum satisfiability problems.