Since 2004 Boeing has booked 787 orders but started delivering in 2011. each year an ideal number is for every unit booked a unit is delivered, thus indicating a 1-1 ratio of Booked to Bill. A graph below shows this relationship. The Blue line is booked (orders) and the orange line is billed (delivered )787. The goal for 2017 is to have the two lines intersect at year's end thus equaling a Book To Bill ratio of one.
The graph below below is an example of Boeing's goal over the last six years since its first delivery was made in 2011. The Book to Bill ratio intersected in 2012 and 2013 during production start-up period. However, in 2017 with the year incomplete there is a possibility the lines will intersect when accounting is done with Boeing's numbers.