Blagged from http://ratatosk.backpackit.com/pub/1836982-debugging-drupal for reference
Prints a variable to the ‘message’ area of the page using drupal_set_message(). You can use this function to keep track of one or more variables when you’re working on the code running your site. Because the Devel module now comes with Krumo, the output is compact and unobtrusive.
dpm($input, $name = NULL)
If, for some reason, you are not using Krumo, you can use the $name parameter to distinguish between different calls to dpm().