condition mean min max ZT0-3 7.303631 7.303631 7.303631 ZT4-7 8.247267 8.247267 8.247267 ZT8-11 7.977456 7.977456 7.977456 ZT12-15 7.690859 7.690859 7.690859 ZT16-19 8.066310999999999 8.066310999999999 8.066310999999999 ZT20-23 7.967936 7.967936 7.967936