It is also possible to declare markers. Markers have no physical connection to the field. There are three types of markers, i.e. digitals, analogues and text.  Functions for digital outputs can also be used for digital markers. This also applies to the analogue markers; functions for analogue outputs can also be used for analogue markers. There is one extra marker type that is different from digital and analogue values. This is the text marker. Text markers can contain text strings. 

Markers are specially usefull for communication with HMI.