diff --git a/bin/logtool b/bin/logtool
index d1fb9fa512a96462b870e00ed14abcfb11dffa70..17ebb32e81a722c6d1c25f16471547f88c0485b5 100755
--- a/bin/logtool
+++ b/bin/logtool
@@ -35,6 +35,10 @@ following:
     parser.add_option("--title", 
             help="Set the title of a plot",
             default="Log evaluation")
+    parser.add_option("--start-step", metavar="STEP", type="int",
+            help="Start the plot at this timestep number")
+    parser.add_option("--end-step",  metavar="STEP", type="int",
+            help="End the plot at this timestep number")
     options, args = parser.parse_args()
 
     if len(args) < 1:
@@ -83,8 +87,10 @@ following:
             expr_x, expr_y = args.pop(0).split(",")
 
             from pylab import xlabel, ylabel, plot
+            print options.start_step, options.end_step
             (data_x, descr_x, unit_x), (data_y, descr_y, unit_y) = \
-                    logmgr.get_plot_data(expr_x, expr_y)
+                    logmgr.get_plot_data(expr_x, expr_y,
+                            options.start_step, options.end_step)
 
             if options.units_x:
                 xlabel(unit_x)
diff --git a/src/log.py b/src/log.py
index ca45f8fc8c08eb701754f9f332f65195be4cc217..d6599ec41ffa7df83ee535da47b2a8c113df1eb5 100644
--- a/src/log.py
+++ b/src/log.py
@@ -289,7 +289,7 @@ class LogManager:
             from pymbolic import substitute, parse
 
             unit = substitute(parsed,
-                    dict((dd.expr, parse(dd.quantity.unit)) for dd in dep_data)
+                    dict((dd.varname, parse(dd.quantity.unit)) for dd in dep_data)
                     )
 
         if description is None:
@@ -383,14 +383,20 @@ class LogManager:
         from cPickle import load
         self.quantity_data, self.constants, self.is_parallel = load(open(filename))
 
-    def get_plot_data(self, expr_x, expr_y):
+    def get_plot_data(self, expr_x, expr_y, min_step=None, max_step=None):
         """Generate plot-ready data.
 
         @return: C{(data_x, descr_x, unit_x), (data_y, descr_y, unit_y)}
         """
         (descr_x, descr_y), (unit_x, unit_y), data = \
                 self.get_joint_dataset([expr_x, expr_y])
-        _, stepless_data = zip(*data)
+        if min_step is not None:
+            data = [(step, tup) for step, tup in data if min_step <= step]
+        if max_step is not None:
+            data = [(step, tup) for step, tup in data if step <= max_step]
+
+        stepless_data = [tup for step, tup in data]
+
         data_x, data_y = zip(*stepless_data)
         return (data_x, descr_x, unit_x), \
                (data_y, descr_y, unit_y)