Temporal interpretation of a changing situation
GRAFCET basic concepts

The IEC 60848 standard specifies that "the intuitive interpretation of evolution, known as "step-by-step", designates the progressive approach which, on occurrence of an input event and starting from the previous situation, makes it possible to determine, by successive application of the evolution rules on each transition, the situation subsequent to the event considered (examples 1 and 2). This ease of interpretation is an artifice permitting indirect specification of evolution, but the specifier must take care that crossing the transitions located on this path does not imply the effective activation of intermediate situations (example 3)".