When it comes to machines in a series, sometimes the "What's the Difference?" question can get a little fickle. For the Bernette 60 series, which includes the Bernette 62 Airlock, Bernette 64 Airlock, and Bernette 68 Airlock, you might be wondering how much of a difference there can be in three machines that are all so great. But each holds a different specialty and at least on…