The template header file contains pure php code. This code is used for checking and setting of needed variables. Template header files are mostly common in their functionality and may be used in most of the template body files.
Template body files contain html and php code. This code is used to fill neccessary values for script- and html-tags. Have a look at "default.php", which is used in most of the samples I've created.
I've marked all php code in green color - you may have detected that most of all variables have been defined by your chart script.
The red color marked include of "default_header.php" has been used to has setup defaults for missing variables (e.g. for "$chart_name", "event_script" or "canvas_style").
Now that you have learnt what rgraph chart-scripts are and how to use templates, you may want to know how to use them on your website.