There is a 'target' bug on the EICAS N1 display, and there is also an 'N1 Command' bug. Manual power set is done by moving the throttles such that the Command bug and the target bug pretty much line up. While the engines are spooling up there is also what we call a 'command sector' - an arc between the N1 actual and the N1 command. Manually setting N1 command to the target is pretty close to trivial (especially on the 777 which has what I believe to be the best throttle Boeing's ever done).
Sadly, if someone never does a manual power set, they likely don't know or have forgotten about it...