Getting average value for a period with RRDTool

I am using RRDTool to fetch data from RRD DB's, but have problem开发者_如何学编程 to get average/max number for a period (e.g. 12 hours). I want only one number representins the average/max of the period as GPRINT does in the graph function.

the trick is to use the graph function but use PRINT instead of GPRINT ... you can even leave out any functions that actually draw to the graph and use the graph function to calculate just the numbers ...

hth tobi