Setting the Format Label

Hi all,
I tried to set the format for the label of the x axis
I tried with

but It did not work.
Do you have any suggestions
Best Regards

The axis labels’ format cannot be changed that way. This function set the format when a histogram is plotted with the option TEXT. The axis labels’ format can be change (a bit) as said in the TGaxis doc:

Format of labels.
   Blank characters are stripped, and then the
   label is correctly aligned. the dot, if last
   character of the string, is also stripped,
   unless the option "." (a dot, or period) is specified.
   if SetDecimals(kTRUE) has been called (bit TAxis::kDecimals set).
   all labels have the same number of decimals after the "."
   The same is true if gStyle->SetStripDecimals(kFALSE) has been called.