condition mean min max ZT0-3 6.403425 6.403425 6.403425 ZT4-7 6.76843 6.76843 6.76843 ZT8-11 7.951465000000001 7.951465000000001 7.951465000000001 ZT12-15 7.8504000000000005 7.8504000000000005 7.8504000000000005 ZT16-19 8.37307 8.37307 8.37307 ZT20-23 6.644155 6.644155 6.644155