condition mean min max ZT0-3 9.081537 9.081537 9.081537 ZT4-7 8.4939845 8.4939845 8.4939845 ZT8-11 9.0116665 9.0116665 9.0116665 ZT12-15 7.972646 7.972646 7.972646 ZT16-19 7.7769205 7.7769205 7.7769205 ZT20-23 8.327428999999999 8.327428999999999 8.327428999999999