Let me first say that, as the developer, John can use whatever he wants to design his project and I don't understand why anyone should be upset about it. If you don't like what he's developed then "roll your own". And with that, I can tell you that because of the way the software is written, while the schematic does call for a 3.2768 MHz crystal, you can substitute either a 3.58 or 4 MHz crystal - which you should have no trouble locating in your junk box. The calibration routine which is built in to the program will allow you to compensate for the freq mismatch. I've tried both.