Hi Tim,
This is already supported in the product by using the {FDATE} and {TDATE} placeholders for the period captions. At runtime, these return the ‘From Date’ and ‘To Date’ of each period in MMM YYYYY format, like this;
If the custom column is using a range of offsets, you could have a dynamic caption by using “Sales {FDATE} to {TDATE}”, which would look like this at runtime;
This technique is covered in the documentation (in the section ‘Note about column names’); https://help.phocassoftware.com/display/userdoc/Custom+mode