 The name is based on the observation that programs in this language resemble ladders, with two vertical rails and a series of horizontal rungs between them.While ladder diagrams were once the only available notation for recording programmable controller programs, today other forms are standardized in IEC 61131-3 (For example, as an alternative to the graphical ladder logic form, there is also a more assembly language like format called Instruction list within the IEC 61131-3 standard.