2008-11 (1989): possible probable confirmed
present 0 - 0.5 0.5 - 1 1 - 1.5 1.5 - 2 2 - 2.5 > 2.5
Count relative to the average of occupied tetrads
present 0 - 0.5 0.5 - 1 1 - 1.5 1.5 - 2 2 - 2.5 > 2.5
Count relative to the average of occupied tetrads