Ignoring Zero Values in Excel Graph

Dear Experts,

I have here attached an excel file for your kind attention and help.

In this report there is an excel graph whose name is "Quality Index Chart May 2016". The data range for this is in "May 2016 Data sheet". My requirement is; "the CURVES should not drop down to "zero" values although the data sheet contains zero values in the range.

Thanks in advance.

Anuruddha