When product demand is sufficiently high and sustainable over a long period of time it is usually cost effective to rearrange resources from a process layout to a product layout as defined by the sequence of steps required to make the product. We often call these assembly lines, although the ratio of direct manual labor to machine work can vary widely. Assembly lines can vary from virtually 100 percent parts assembly by workers. to the other extreme, an automated transfer line. where all direct work is done by machine. In between are all types Auto.mobile lines have tools ranging from simple hammers and wrenches fa robotic welding and painting. Assembly lines in electronics also can range widely from manual parts assembly to equipment for automatic parts insertion automatic soldering and automatic testing.