While there are many important pieces of equipment that go into making a great cup of coffee the most important is without a doubt the grinder. While this may seem like a bold statement, don't fear! It's not to say that a high end espresso machine or a hand-blown chemex aren't important, more so that without a good grinder beforehand, their inherent advantages can be over shadowed by a poorly extracted coffee as a result of uneven grind size. Just how does the evenness of a grind affect extraction? Let's turn to what I'll refer to as "Particle Size Distribution" or PSD for short.
What is PSD?
In a nut shell, PSD refers to the spread of different particle sizes produced by a given grinder, and what portion of the whole sample each size represents. It's easy to think that by adjusting our grinder to a given grind size we end up with an even, and consistent PSD, but in reality we always end up with a full spread ranging from "fines" (that dust-like super fine powder) to "boulders" which happen when oddly shaped pieces slip through the burrs without first being broken down further.
Have a look at the diagrams below for a little more info on how an even Particle Size Distribution can result in even extraction and a much more balanced cup.