smooth() doesn't specify units (ie, pixels for position, etc).
The two arguments are width and samples.
Esoteric? I know
The best explanation I saw is in Mark Christiansen's amazing "After Effects CS4 Studio Techniques" book:
"Width determines how much time (before and after the current time) is averaged to create the result. A setting of 2 samples 2 seconds means 1 second before and 1 second after the current time. The samples argument determines how many individual points within that range are actually sampled for the result; generally, the more samples, the smoother the curve".
Posted by Adolfo Rozenfeld @ adobe AE user to user forum
