diff -Naur ChartPlugin_20021011/lib/TWiki/Plugins/ChartPlugin/Chart.pm ChartPlugin_20021011_local/lib/TWiki/Plugins/ChartPlugin/Chart.pm
--- ChartPlugin_20021011/lib/TWiki/Plugins/ChartPlugin/Chart.pm	Thu Oct 10 19:05:47 2002
+++ ChartPlugin_20021011_local/lib/TWiki/Plugins/ChartPlugin/Chart.pm	Sat Jul  5 13:09:23 2003
@@ -140,7 +140,7 @@
     setDataTypes getDataTypes
     setXaxis getXaxis
     setYaxis getYaxis
-    setNumYGrids getNumYGrids
+    setNumYGrids getYLog setYLog getNumYGrids
     setXgrid getXgrid
     setYgrid getYgrid
     setDataLabels getDataLabels
@@ -176,6 +176,7 @@
     $this->setFont("legend", GD::gdSmallFont());# Set legend font
     $this->setFont("data", GD::gdSmallFont());	# Set data values font
     $this->setNumYGrids(10);
+    $this->setYLog("off");
     $this->setNumDigits(0);
     return $this;
 }
@@ -267,6 +268,22 @@
 sub setNumYGrids { my ($this, $numYGrids) = @_; $$this{NUM_Y_GRIDS} = $numYGrids; }
 sub getNumYGrids { my ($this) = @_; return $$this{NUM_Y_GRIDS}; }
 
+sub setYLog { my ($this, $YLog) = @_; $$this{Y_LOG} = $YLog; }
+sub getYLog { my ($this) = @_; return $$this{Y_LOG}; }
+
+sub ifylog {
+  my ($this, $val) = @_;
+  my $orig=$val;
+  if ( $$this{Y_LOG} eq "on" ) {
+    if ($val > 0) {
+      $val=log($val)/log(10);
+    } else {
+      $val=0;
+    }
+  }
+  return $val;
+}
+
 sub setXgrid { my ($this, $xGrid) = @_; $$this{X_GRID} = $xGrid; }
 sub getXgrid { my ($this) = @_; return $$this{X_GRID}; }
 
@@ -449,6 +466,8 @@
     my $imageWidth = $this->getImageWidth();
     my $imageHeight = $this->getImageHeight();
 
+    my $yLog = $this->getYLog();
+
     # Create empty image to get filled in later.
     my $im = new GD::Image($imageWidth, $imageHeight);
     $this->setImage($im);
@@ -479,8 +498,8 @@
     my @allocatedColors = $this->computeFinalColors();
 
     # Get the Y min/max values to be charted.
-    my $yMin = $this->getYmin();
-    my $yMax = $this->getYmax();
+    #my $yMin = $this->ifylog($this->getYmin());
+    #my $yMax = $this->ifylog($this->getYmax());
 
     # Calculate the initial pixel locations of lower left side (xLL/yLL)
     # and upper right side (xUR/yUR) of the chart with respect to the
@@ -517,9 +536,15 @@
 	# number of digits to use when displaying the Y axis labels.
 	$this->computeNumDigits();
     }
-    $yAxisMin = $this->getYminOfData() if (! defined($yAxisMin));
-    $yAxisMax = $this->getYmaxOfData() if (! defined($yAxisMax));
-    $numYGrids = $this->getNumYGrids();
+    $yAxisMin = $this->ifylog($this->getYminOfData()) if (! defined($yAxisMin));
+    $yAxisMax = $this->ifylog($this->getYmaxOfData()) if (! defined($yAxisMax));
+    if ($yLog eq "on") { $yAxisMax = int($yAxisMax) + 1; }
+
+    if ($yLog eq "on") {
+      $numYGrids = int($yAxisMax);
+    } else {
+      $numYGrids = $this->getNumYGrids();
+    }
     $yAxisDecimalDigits = $this->getNumDigits();
     my $chartHeight = $yAxisMax - $yAxisMin;
     # Check to see if either the user specified ymin/ymax values, or the
@@ -546,11 +571,16 @@
 	my $maxLength = 0;
 	my $len;
 	for my $yAxisIndex (0..$numYGrids) {
-	    my $text = _printNumber($yaxis, $yAxisDecimalDigits);
-	    $yLabels[$yAxisIndex] = $text;
-	    $len = length ($text);
-	    $maxLength = $len if ($len > $maxLength);
-	    $yaxis += $labelInc;
+	  my $text = "";
+	  if ($yLog eq "on") {
+	    $text = _printNumber(10 ** $yAxisIndex, $yAxisDecimalDigits);
+	  } else {
+	    $text = _printNumber($yaxis, $yAxisDecimalDigits);
+	  }
+	  $yLabels[$yAxisIndex] = $text;
+	  $len = length ($text);
+	  $maxLength = $len if ($len > $maxLength);
+	  $yaxis += $labelInc;
 	}
 	$xLL += $this->getFontWidth("yaxis") * $maxLength;
     }
@@ -616,8 +646,8 @@
 	my $color = $allocatedColors[$dataSet];
 	# Draw the line (if an area, it gets filled in below).
 	for my $xIndex (0..($numDataPoints - 2)) {
-	    my $currentValue = $row[$xIndex];
-	    my $nextValue = $row[$xIndex + 1];
+	    my $currentValue = $this->ifylog($row[$xIndex]);
+	    my $nextValue = $this->ifylog($row[$xIndex + 1]);
 
 	    my $x1 = $xLL + ($xDrawInc * $xIndex);
 	    my $y1 = $yLL - ($currentValue - $yAxisMin) * $yPixelsPerValue;
@@ -641,8 +671,8 @@
 	# area that has separate regions.
 	if ($dataTypes[$dataSet] eq "area") {
 	    for my $xIndex (0..($numDataPoints - 2)) {
-		my $currentValue = $row[$xIndex];
-		my $nextValue = $row[$xIndex + 1];
+		my $currentValue = $this->ifylog($row[$xIndex]);
+		my $nextValue = $this->ifylog($row[$xIndex + 1]);
 		my $x1 = $xLL + ($xDrawInc * $xIndex);
 		my $y1 = $yLL - ($currentValue - $yAxisMin) * $yPixelsPerValue;
 		my $x2 = $xLL + ($xDrawInc * ($xIndex + 1));
diff -Naur ChartPlugin_20021011/lib/TWiki/Plugins/ChartPlugin.pm ChartPlugin_20021011_local/lib/TWiki/Plugins/ChartPlugin.pm
--- ChartPlugin_20021011/lib/TWiki/Plugins/ChartPlugin.pm	Fri Oct 11 10:12:17 2002
+++ ChartPlugin_20021011_local/lib/TWiki/Plugins/ChartPlugin.pm	Sat Jul  5 13:09:16 2003
@@ -333,6 +333,9 @@
     # See if the parameter 'numygrids' is available.
     $chart->setNumYGrids( $this->_Parameters->getParameter( "numygrids", $defaultNumYGrids) );
 
+    # See if the parameter 'numygrids' is available.
+    $chart->setYLog( $this->_Parameters->getParameter( "ylog", "off") );
+
     # See if the parameter 'xgrid' is available.
     my $xGrid = $this->_Parameters->getParameter( "xgrid", "dot");
     $chart->setXgrid($xGrid);