jquery - Show date in jqplot tooltip -

i using jquery jqplot(bar chart) ruby on rails application. sending date apr, 2012 , amount in dollars chart. on bar mouseover tooltip showing date index i.e [1, $200], [2,$300] instead of date(apr,2013). how can replace index date?? date on x-axis , amount on y-axis. here highlighter code:

highlighter:   show: true   showmarker: false   formatstring: '<table class="jqplot-highlighter">                  <tr><td><b>%s</b></td><td><b>%s</b></td>                  </tr></table>' 

did added js?

<script type="text/javascript" language="javascript" src="plugins/jqplot.dateaxisrenderer.js"></script> 

and try this:

highlighter: {     tooltipaxes: 'y',     yvalues: 2,     formatstring: '<table class="jqplot-highlighter">                      <tr><td><b>%b</b></td><td><b>,%y</b></td>                      </tr></table>' } 

more details.