condition mean min max ZT0-3 7.820455 7.820455 7.820455 ZT4-7 7.6458705 7.6458705 7.6458705 ZT8-11 7.935539500000001 7.935539500000001 7.935539500000001 ZT12-15 7.142551 7.142551 7.142551 ZT16-19 8.226078999999999 8.226078999999999 8.226078999999999 ZT20-23 7.6929545 7.6929545 7.6929545