Here is a little background on Industry acronyms: Historically, in the US, military requirements have been the main impetus for research on “crystal oscillators.” The US Army sponsored most of the research, especially in the early days. According to folklore, the abbreviation XO instead of CO came about because, in the military, CO is the abbreviation for "commanding officer" and because "crystal" sounds a little like "xtal". The rest of this module will focus on SAW oscillators, although Epson offers all the other high-end oscillators as well.