→Constant

according to →IEC-standard: language element which declares a data element with a fixed value

In the ST-editor, constant →variables are declared by using the keyword CONSTANT . This keyword is only allowed for the sections VAR, VAR_GLOBAL and VAR_EXTERNAL.
In the FBD-editor, constant variables are declared by using the prefix C (in particular when creating a value field with a new variable). This prefix is only allowed for internal variables, →global variables and →external variables.