# Changes

$Pe = \frac{(Convection \, rate)}{(Diffusion \, rate)} = \frac {UL}{D}$ U represents linear flow in a control volume, L represents the length scale of the flow and D is the diffusion constant. This number can also be represented as a ratio of diffusive to convective time scales.
$Pe = \frac{(Diffusion \, timescale)}{(Convection \, timescale)}$