In a productive context characterized by the presence of manual work, and in this specific case within an Assembly-To -Order (ATO) environment, one of the biggest problems is related to the discrepancy between what is planned and what really happens. This is linked to the presence of an enormous variability within the activities of the assembly process.Through the case study of a particular business, some specific and correct data were collected to ensure that good planning could give control over the planned activities. But, since the variability is inherent to the activities related to human presence, it is necessary to have a method that standardizes the production and consequently controls the processes to be able to ensure optimal planning: this is the core foundations of “Lean house”, and therefore Lean Manufacturing (LM) is a suitable consideration.The researchers have not yet found a definitive Production, Planning and Control (PPC) method for the hybrid environment ATO: they are still using readjustments of either Make-To-Stock (MTS) or Make-To-Order (MTO). Again, the presence of human operators in the process makes it more difficult to complete precise planning.After all the data needed to understand the planning was found and analyzed, it appears clearly that the variability is such that it cannot be eliminated by the manual process unless the process is first stabilized and standardized.The recommendations here are based on the principles set out by Lean and industry 4.0 technology tools. Using these tools will allow the company to improve production and allow greater consistency with respect to the date of delivery (due date) of the finished product to customers. Future research will have to consider, after the application of the methods mentioned above, the introduction of the skills of the operators in the planning and therefore an updated plan.