condition mean min max ZT0-3 6.1 6.1 6.1 ZT4-7 8.0 8.0 8.0 ZT8-11 9.0 9.0 9.0 ZT12-15 31.6 31.6 31.6 ZT16-19 10.0 10.0 10.0 ZT20-23 8.65 8.65 8.65