How accurate is the Traffic Graph?

[Maniax]

I've been playing with limiters and using the Traffic Graph to get a feel for how they are working. Using the LAN interface setting on the Traffic Graph I frequently see individual network clients exceed the limiter I have applied to them (by 1-3Mbit sometimes).

Are the Traffic Graph numbers accurate?

I'm pretty positive I have the limiters setup correctly but the graph/table showing clients exceeding them confounds me.

Thanks!