Originally Posted by
HillRider
They help you center the bars in the stem clamp and give you an index to set the angle of the drops and hooks. There are bars with index marks on the bends to assist brake lever/brifter placement
Uhhh, you don't carry the broom handle, it stays in the shop.

Frankly, the broom handle/yardstick method of equalizing lever placement is a lot more convenient than standing the bike on it's head to use the floor for the same purpose.
Adjusting angle is purely by feel, I don't see how those + 0 - lines help. You ride around and make adjustments.
What I meant by "starting from scratch" was handlebars off the bike.