For each year from 1970 up to last year, list your fav metal album released that year + your fav non-metal album from the same year, and pick the better of the two. Then calculate the % of years where metal won the head to head battle to get your score. For example, picks bolded here would mean a score of 50% metal so far: '70: Black Sabbath – Paranoid .......... Miles Davis – Bitches Brew '71: Black Sabbath – Master of Reality .......... Led Zeppelin – IV '72: Deep Purple – Machine Head .......... Wishbone Ash – Argus '73: Budgie – Never Turn Your Back on a Friend .......... Pink Floyd – Dark Side of the Moon ...and on it goes. Might be best to put such long lists in spoiler tags (or not). Usual blah blah about using some of your own discretion to figure out which side borderline albums should go on.