This "quick tutorial" introduces the general idea of a call and explains the most common cases. It does not explain or illustrate all cases. For additional details and/or examples, refer to the links in the "MORE INFO" box.
From parallel two-faced lines, the trailers move as if they were doing an All 8 Circulate combined with a Half Sashay. They both move forward, but as they are walking across the belle (the dancer on the right) slides in front of the beau (the dancer on the left). Meanwhile, the leaders individually turn and walk toward the other half of the line and then face in, with the original center walking all the way to become the new end and the original end becoming the new center.
Another way of looking at this is that each dancer ends up where they would have ended up if they were part of a couple doing an All 8 Circulate combined with a Half Sashay. But notice that they don't necessarily move that way. In the case of parallel two-faced lines, the leaders don't need to do anything that looks or feels like a Half Sashay, because they naturally switch places as part of walking individually to the other half of the line.
From facing lines, Cross Over Circulate is just like a Cross Trail Thru for everybody.
From back-to-back lines, all the dancers are turning and walking toward the other half of their line, and they pass right shoulders with the dancers coming the other way. In this case, they are all moving as if they were doing a Tag the Line and Face In.
Cross Over Circulate is also often commonly done from parallel waves. In this case, the dancers who are facing in move as if they were doing a diagonal Pass Thru, passing right shoulders with the dancer coming the other way. The dancers who are facing out do the equivalent of a Trade with each other, also passing right shoulders.