Nobody mentioned it here but one thing that you will quickly learn when you tie leaders is how much extra line you need for the knot. So when you cut off a section of line it needs to be longer than the length of line in the formula. I've found that I need to add ~5-6" extra per blood knot to the segment length.
And from experience don't cut all the sections for multiple leaders ahead of time. It can be a fun job figuring out what is what after the child picks them all up and runs around asking whats this dad? .