Dear Sir..Thanks for helping...but I was not able to get the point...whether that xls sheet is some software? In literature concerned in plant physiology (journal) I get the information that with infra red gas analyser portable system we can estimate compensation point...but authors did not give back references that how they determine it. We are planning for research related to diff. c3 and c4 species of same genus..We have portable photosynthesis system but how I measure co2 compensation point with it's help. ..I don't know.. You have also said ref in api....What does it mean? Api is some journal name??