Tartine Loaf: The Formula
There's been some discussion about the baker's percentage formula for the Tartine Loaf in Chad Robertson's book. I thought I'd create a spreadsheet that clarified the formula. As related on page 48 of his book, he gives the baker's percentage but only in terms of the final ingredients. The formula doesn't include the flour and water in the leaven. So while he states the bread has a 75% hydration, it is actually higher, 77% The formula also makes it difficult to convert the recipe into smaller loaves. So I've created a spread sheet that does that, following a method at the Bread Bakers Guild of America. The measurements are all in grams.
The spreadsheet shows the TOTAL formula in the left column and the FINAL formula which mirrors Robertson's. To use this spreadsheet, I've made it available in google docs. 
The nice thing about it is that you enter the number of loaves and the size of loaves (THE FIRST TWO CELLS -- NOTHING ELSE). The spreadsheet figures out the rest -- which is highlighted in blue.
I've only given the total leaven you need (white, whole wheat and water). The seed for that leaven should be only a couple of tablespoons. One more note -- the fourth line of the spreadsheet shows the "% flour levain" -- which means the percentage of total flour that is prefermented in the leaven. Many formulas go as high as 40%. Robertson's is much lower, which means the leaven takes longer to mature and has a much milder taste. As I noted before , however, the fermentation is spurred by the presence of whole wheat flour at 50% in the leaven.
So ultimately does it matter, getting the precise formula? I would say no. But this is it. Now you can make it your own.