A visual check on the quality of componets,materials,and accessories at the beginning of production against clients' specifications and reference sample. The  PPI thus permits timely  corrections and improvements  before the mass production is initiated and any non-conformity is immediately reported so as to avoid delay in shipment.? In general, we will check the following aspects for PPI:
Evaluate the production capability and equipments in the factory
Check factory's quality control ability and executive status
Check the accuracy of production facilities and equipments
Audit production techniques and make sure the reasonable layout of factory
Check the quantity and quality of raw materials and main components that will be used in your products,foreseeing any possible problems to avoid them,verifying  that your product specifications are being met early.