condition mean min max ZT0-3 7.400907 7.400907 7.400907 ZT4-7 8.66411 8.66411 8.66411 ZT8-11 8.374852 8.374852 8.374852 ZT12-15 7.9113085000000005 7.9113085000000005 7.9113085000000005 ZT16-19 8.564624 8.564624 8.564624 ZT20-23 8.143172499999999 8.143172499999999 8.143172499999999