Prechac patterns

Prechac patterns are staggered symmetric passing patterns, meaning two or more jugglers do the same sequence of throws, but at different times. When one person is starting a cycle of a 2-person Prechac pattern, the other person is halfway through that same cycle of throws. The concept behind these patterns was first described by Christophe Prechac in 1999.
Any solo siteswap can be turned into a 2-person Prechac pattern by either adding or subtracting half the period of the pattern to any number in the pattern and making that throw a pass. You can transform as many throws as you want this way. (This gives you the pattern in a simplified notation that only tells you what each juggler does individually. The full siteswap notation describing the whole passing pattern would be a little more complicated.) A 2-person Prechac pattern made by adding half the period to an N object pattern is done with 2N + 1 objects, and a 2-person Prechac pattern made by subtracting half the period from an N object pattern is done with 2N - 1 objects.
A 2p in a Prechac pattern is often done by lifting the object up and dropping it vertically into the other person's hand. A 1p can be done by turning your palm to face down as you place the object into your partner's palm, which is facing up.
Example: Half the period of the solo pattern 4413 is 2. Subtracting 2 from the second 4, you get 42p13, which can be done as a 2-person Prechac pattern with 5 balls. The 2 ball is lifted up diagonally while throwing the 4, and then dropped from one person's left hand into the other person's left hand. The second person waits for the first person to do the first two throws, and then starts with a 4 at the same time as the first person is doing a 1.
== Fractional throws ==
If the period of the original solo siteswap is an odd number, the 2-person Prechac pattern you end up with will contain throws with fractional siteswap values. Fractional siteswap numbers don't work in solo patterns, because that would mean you would have to throw the object again halfway between two consecutive throws (which would make those throws not actually be consecutive). But they do work in a staggered passing pattern based on a solo siteswap with an odd period, because now one person's throws are being made halfway in between the other person's throws.
The same fractional siteswap number will mean a straight pass when done by one juggler and a diagonal pass when done by the other juggler within the same pattern. If your right hand throws are followed by throws from your partner's right hand, a throw that is an odd number + 1/2 is a straight pass, and a throw that is an even number + 1/2 is a diagonal pass. If your right hand throws are followed by throws from your partner's left hand, a throw that is an odd number + 1/2 is a diagonal pass, and a throw that is an even number + 1/2 is a straight pass.
Example: Half the period of the solo pattern 531 is 1.5. Subtracting 1.5 from the 5, you get 3.5p 3 1, a 5 ball Prechac pattern. The second person starts throwing halfway between the first person's 2nd and 3rd throws. If both people start with their right hands, the first person will be making diagonal passes, and the second person will be making straight passes.
== 3-person patterns ==
To turn a solo siteswap into a 3-person Prechac pattern, add or subtract 1/3 (or 2/3) of the period to any throw and make it a pass.
If a passed throw in a 3-person Prechac pattern is 1/3 of the period higher (or 2/3 of the period lower) than the number in the solo pattern it was derived from, that throw is passed to the person whose turn to pass comes next. If the throw was calculated by subtracting 1/3 of the period (or adding 2/3 of the period), then it's passed to the person who just did the preceding pass.
==External links==
*Staggered Symmetric Passing by Sean Gandini
*Prechac This - a Prechac pattern generator
*Animating Odd Period Staggered Symmetric (Prechac) Passing Patterns with Juggling Lab
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Category:Patterns
Category:Passing patterns