Pretty much like this (I know this isn't accurate but it's a mock up).
It would really help when you're uncertain as to how much the song is off.
i would like to have - or +, or maybe ← and → so i know if i am early or too lateThe middle white line is 0, anything to the right is late and anything to the left is early. The white arrow indicates an average of where you're hitting but it's kind of vague looking at a bar without any numerical representation to it. Having a small integer above the white arrow (or in the middle line with a +/- as you described) would be very useful in determining an offset when you're absolutely certain you're hitting the notes correctly.