How are the polling stats calculated

[Diskbox]

I've just been asked by someone how these are calculated and it just occurred to me that I don't know.

How are things like network and processor usage calculated using the built in templates?

Do they poll every 5 minutes and take a quick snap-shot of what the current usage is then post that to cacti and work out an average for the 5 mins or

Do they somehow collect 5 mins worth of data and post that to cacti?

Have had a bit of a dig around but can't seem to fine a definitive answer anywhere.

[gandalf]

That depends.
There are OIDs that are defined as GAUGEs. Thise take the current value of whatever they are representing.
A better soltion in general are COUNTERs. They take the complete change of the last polling interval into account. See e.g. 1st link of my sig, RRDTool chapter, for more explanations
R.