I use index cards. Turn the wheel to lower the needle into one of the lines. Look to the right to see how far off your foot is. (edge of foot should be exactly on the line to the right.) If it needs adjustment, adjust your needle (right or left).
This is also great if trying to achieve a scant 1/4".
Every machine has a different needle placement for a true 1/4". (I don't have to use the 1/4" foot, which isn't very accurate anyway.)