condition mean min max ZT0-3 8.162529 8.162529 8.162529 ZT4-7 8.3908865 8.3908865 8.3908865 ZT8-11 7.881209999999999 7.881209999999999 7.881209999999999 ZT12-15 8.7388645 8.7388645 8.7388645 ZT16-19 7.813981999999999 7.813981999999999 7.813981999999999 ZT20-23 8.372366 8.372366 8.372366