condition mean min max ZT0-3 7.802867 7.802867 7.802867 ZT4-7 9.939308 9.939308 9.939308 ZT8-11 8.544411499999999 8.544411499999999 8.544411499999999 ZT12-15 8.747478999999998 8.747478999999998 8.747478999999998 ZT16-19 8.532439499999999 8.532439499999999 8.532439499999999 ZT20-23 8.3125885 8.3125885 8.3125885