In a scale there is 8 full notes(whole step) or 12 halv notes(half steps). One
easy way to find the perfect match is to use the chromatic scale rather the the
chart overlay. Simply count 5(sub dominant)or 7(dominant) halfsteps either up or
down the scale. Say that you have a track that is in E major, counting 5 and 7
halfsteps will give you the perfect match, A major and B major.
These 12 notes represent a octave on the keyboard. The "#" and "b" are the black
keys on the keyboard. Before the camelot system the cromatic scale was the
quickest way to find harmonical matches.