****************************************
Short helpfile for action MEAN
****************************************

The following arguments are compulsory: 

               PERIODIC - if the output of your function is periodic then you should 
                          specify the periodicity of the function. If the output is not 
                          periodic you must state this using PERIODIC=NO 
                    ARG - the input to this function. You can use multiple instances 
                          of this keyword i.e. ARG1, ARG2, ARG3... 


