The Starting Chain Formula is calculated by figuring out how many stitches are needed for each design repeat in that pattern plus any extra chains needed for the first turning chain plus any extra stitches that are given in the pattern directions for edge stitches that are done before the design repeat begins and for edge stitches that are done after the design repeat ends at the other edge.
Following are some examples.
What does it mean to crochet a "multiple of 6 plus 4"?
To chain a "multiple of 6 plus 4", multiply 6 times another number, then add four more.
Examples:
6 x 2 = 12 plus 4 = a total of 16
6 x 3 = 18 plus 4 = a total of 22
... and so forth.
What does it mean to crochet a "multiple of 12 plus 1"?
To chain a "multiple of 12 plus 1", multiply 12 times another number, then add one more.
Examples:
12 x 2 = 24 plus 1 = a total of 25
12 x 3 = 36 plus 1 = a total of 37
... and so forth.
Examples of some patterns that give a Starting Chain Formula:
Cross-Over Long Double Crochet - http://crochet.about.com/od/learnmorestitches/tp/skcrdc.htm
Cross-Over Shells - http://crochet.about.com/library/weekly/aa012399.htm
Open Shell Edging - http://crochet.about.com/library/weekly/aa032501.htm
Photo How-To For Diagonal Shell - http://crochet.about.com/library/weekly/aa071198.htm
