Charts - Legends

I have drawn a chart inside my excel sheet which has my data.

Now the legends are selected from the same table - from row headings.

These legends in my table are formatted like S0, S1, ... where 0 and 1 are subscripts.

When the chart is drawn, these legends appear as normal text - they lose the subscript formatting.

I need help to get the format correctly. Below is a sample.

In the above table, System column is the legend - here also the subscript is not shown.

Thank you.