fractal
(Hausdorff dimension?)
discretely, it's "change from one scale to another"
esp. useful if trying to make dimension of a fat/discrete set
[eg, price movements]
general principle:
given s'thing defined via limit (deriv),
can also study steps, yielding sequence etc.
[tangent line -> secant line;
get Lifschitz functions etc.]
can also have lim sup, lim inf