We'll describe calculus on two fractal sets: the unit interval and the Vicsek set. Integration is pretty straightforward, but differentiation is hard; we can only define a second derivative (a Laplacian). Fortunately, in both cases we have spectral decimation, a powerful algorithm which allows us to recursively construct both the eigenvalues and eigenfunctions of the Laplacian. Along the way we'll relate all this to resistor networks from high school physics, and maybe even learn something new about sine and cosine.