condition mean min max ZT0-3 18.589021 18.589021 18.589021 ZT4-7 18.438306 18.438306 18.438306 ZT8-11 18.9391495 18.9391495 18.9391495 ZT12-15 21.054850000000002 21.054850000000002 21.054850000000002 ZT16-19 18.972974 18.972974 18.972974 ZT20-23 21.0719135 21.0719135 21.0719135