The word mark, followed by number, is a method of designating a version of a product. The kind of products that use this convention vary widely in complexity. The concept shares some similarities with both the "Type (designation)" (Hardware) and the  1.0+ (1.1, 1.12, 2.0, 3.0, etc.) Software versioning convention often used to designate general software product releases. It is often abbreviated as Mk or M. Because a is often made to measure height or progress, by metonymy the word mark is used to note a defined level of development thus designations like "Mark I", "Mark II", "Mark III", "Mark IV", etc. come to be used as proper names. However, since the same name is used for a wide variety of products, it can have varied connotations for different persons.