Machines: Tools and equipment used to complete production task. Facility systems also fall into this category.
Methods: Production and support processes.
Materials: Raw materials, components, and supplies used for production. General materials used for business operations (i.e. cleaning supplies, 5S supplies, etc.) also fall into this category.
Mother Nature: Weather and other natural, uncontrollable events fall into this category. Environmental systems (i.e. AC, heating) would likely fall into machines.
Manpower: People issues fall into this area. Note that many people issues are really methods, machine, or material issues. Also note that “manpower”, being gender specific, can be perceived as being insensitive. Some people replace the term with “People Power”.
Measurements: Measurements include physical measurement, automatic sensor readings, and inspections. Note that there may be overlap with machines regarding the measuring devices.