condition mean min max ZT0-3 8.31443 8.31443 8.31443 ZT4-7 7.5865355 7.5865355 7.5865355 ZT8-11 8.038198999999999 8.038198999999999 8.038198999999999 ZT12-15 7.675967 7.675967 7.675967 ZT16-19 8.768050500000001 8.768050500000001 8.768050500000001 ZT20-23 7.914269 7.914269 7.914269