source: trunk/xgraph/jpgraph/Examples/barformatcallbackex1.php

<?php // content="text/plain; charset=utf-8"
require_once ('jpgraph/jpgraph.php');
require_once ('jpgraph/jpgraph_bar.php');

$data = array(0.1235,0.4567,0.67,0.45,0.832);

// Callback function
// Get called with the actual value and should return the
// value to be displayed as a string
function cbFmtPercentage($aVal) {
    return sprintf("%.1f%%",100*$aVal); // Convert to string
}

// Create the graph. 
$graph = new Graph(400,300);    
$graph->SetScale("textlin");

// Create a bar plots
$bar1 = new BarPlot($data);

// Setup the callback function
$bar1->value->SetFormatCallback("cbFmtPercentage");
$bar1->value->Show();

// Add the plot to the graph
$graph->Add($bar1);

// .. and send the graph back to the browser
$graph->Stroke();
?>