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.
First the ends do an arm turn 1/2 (trade) with the adjacent centers, becoming the new centers. They then cast off 3/4 in the center, and then the very center two trade with each other. (Note that this much is the same as the first three parts of Spin Chain Thru.)
But meanwhile, the dancers who originally started in the center, and are now the ends, "flip" back in toward the center. They turn around half way (180 degrees) toward the centers, and move inward toward the centers, as if they were doing an Ends Run. They join the centers to form a four-person star.
These stars are the "gears". Each star then turns 3/4 (three positions) around its own center. This brings one of the dancers who "flipped" -- the one who was facing out after the flip -- into the very center. (Note that up to this point everything is the same as for Spin Chain the Gears.)
The dancers in the very center then lead the rest of the dancers from their own star in an "exchange" of the stars, following an S-shaped path around the outside of the other star. Each dancer who reaches the very center moves up to the next position in the other star, while the dancers who haven't yet reached the very center just continue moving up to the next position in their original star.
After the dancers have moved along three positions in the "exchange" action (a total of six positions including the three when they were just turning in their own star), they form new waves. Dancers #1 and #3, who at this point are standing at the spots that will be the ends of about-to-be-formed waves, "flip in" (again, like an Ends Run) to become the centers of the new waves, and take hands with each other. Meanwhile #2 and #4 simply move up one more position and take hands with the others to become the ends of the new waves.
This is easier than it may sound, because it happens in one continuous motion, with the turning of each star flowing into the exchange and then the formation of the new waves. The dancers don't stop at any of the intermediate positions.
The dancer who is going to "lead the exchange" customarily raises a hand to indicate this, and the other three simply follow that dancer single file, like a parade, first around the center of their own star and then around the original location of the other star, beginning to form a new star around the old one.
Once the dancers have switched their focus to the new star, going around that with a new "inside hand", and far enough to be near the place where they will form the new wave, #1 and #3 need only to turn around halfway and take that hand with the dancer who is following to form a mini-wave. #1 joins that hand with #2 to form one mini-wave, while #3 joins hands with #4 to form another mini-wave, and #1 and #3 join their other hands to complete the whole four-person wave.
Note that the new waves are formed on the same spots where the original waves were located, and have the same handedness.