diff --git a/bin/weeplot/genplot.py b/bin/weeplot/genplot.py
index 0a47e57a..b22cd9e0 100644
--- a/bin/weeplot/genplot.py
+++ b/bin/weeplot/genplot.py
@@ -581,7 +581,7 @@ class TimePlot(GeneralPlot) :
             self.xscale = weeplot.utilities.scaletime(xmin, xmax)
 
     def _calcXLabelFormat(self):
-        """Specialized version for time plots."""
+        """Specialized version for time plots. Assumes that time is in unix epoch time."""
         if self.x_label_format is None:
             (xmin, xmax) = self._calcXMinMax()
             if xmin is not None and xmax is not None:
@@ -594,6 +594,7 @@ class TimePlot(GeneralPlot) :
                     self.x_label_format = u"%X"
         
     def _genXLabel(self, x):
+        """Specialized version for time plots. Assumes that time is in unix epoch time."""
         if self.x_label_format is None:
             return u''
         time_tuple = time.localtime(x)
diff --git a/bin/weewx/imagegenerator.py b/bin/weewx/imagegenerator.py
index 686f16f9..b3c18217 100644
--- a/bin/weewx/imagegenerator.py
+++ b/bin/weewx/imagegenerator.py
@@ -204,9 +204,7 @@ class ImageGenerator(weewx.reportengine.ReportGenerator):
                             stop_vec_t[1],                                          # Unit
                             stop_vec_t[2])                                          # Unit group
 
-                    # Do any necessary unit conversions:
-                    new_start_vec_t = self.converter.convert(start_vec_t)
-                    new_stop_vec_t  = self.converter.convert(stop_vec_t)
+                    # Convert the data to the requested units
                     new_data_vec_t = self.converter.convert(data_vec_t)
 
                     # Add a unit label. NB: all will get overwritten except the last. Get the label
@@ -244,7 +242,7 @@ class ImageGenerator(weewx.reportengine.ReportGenerator):
                             if vector_rotate_str is not None else None
                     elif plot_type == 'bar':
                         interval_vec = [x[1] - x[0] for x in
-                                        zip(new_start_vec_t.value, new_stop_vec_t.value)]
+                                        zip(start_vec_t.value, stop_vec_t.value)]
                     elif plot_type == 'line':
                         gap_fraction = to_float(line_options.get('line_gap_fraction'))
                         if gap_fraction is not None and not 0 < gap_fraction < 1:
@@ -265,7 +263,7 @@ class ImageGenerator(weewx.reportengine.ReportGenerator):
                     
                     # Add the line to the emerging plot:
                     plot.addLine(weeplot.genplot.PlotLine(
-                        new_stop_vec_t[0], new_data_vec_t[0],
+                        stop_vec_t[0], new_data_vec_t[0],
                         label         = label,
                         color         = color,
                         fill_color    = fill_color,