diff -ur cacti-0.8.6b-orig/lib/graph_variables.php cacti-0.8.6b/lib/graph_variables.php
--- cacti-0.8.6b-orig/lib/graph_variables.php	2004-10-27 01:32:56.000000000 +0200
+++ cacti-0.8.6b/lib/graph_variables.php	2004-10-27 01:26:19.000000000 +0200
@@ -78,7 +78,7 @@
    @arg $ds_steps - how many seconds each period represents
    @returns - (array) an array containing each data source item, and its sum */
 function bandwidth_summation($local_data_id, $start_time, $end_time, $rra_steps, $ds_steps) {
-	$fetch_array = rrdtool_function_fetch($local_data_id, $start_time, $end_time);
+	$fetch_array = rrdtool_function_fetch($local_data_id, $start_time, $end_time, $rra_steps * $ds_steps);
 
 	if ((!isset($fetch_array["data_source_names"])) || (count($fetch_array["data_source_names"]) == 0)) {
 		return;
diff -ur cacti-0.8.6b-orig/lib/rrd.php cacti-0.8.6b/lib/rrd.php
--- cacti-0.8.6b-orig/lib/rrd.php	2004-10-27 01:32:56.000000000 +0200
+++ cacti-0.8.6b/lib/rrd.php	2004-10-27 01:31:52.000000000 +0200
@@ -315,7 +315,7 @@
    @returns - (array) an array containing all data in this data source broken down
 	 by each data source item. the maximum of all data source items is included in
 	 an item called 'ninety_fifth_percentile_maximum' */
-function &rrdtool_function_fetch($local_data_id, $start_time, $end_time) {
+function &rrdtool_function_fetch($local_data_id, $start_time, $end_time, $resolution = 0) {
 	if (empty($local_data_id)) {
 		return;
 	}
@@ -326,7 +326,11 @@
 	$data_source_path = get_data_source_path($local_data_id, true);
 
 	/* build and run the rrdtool fetch command with all of our data */
-	$output = rrdtool_execute("fetch $data_source_path AVERAGE -s $start_time -e $end_time", false, RRDTOOL_OUTPUT_STDOUT);
+	$cmd_line = "fetch $data_source_path AVERAGE -s $start_time -e $end_time";
+	if ($resolution > 0) {
+		$cmd_line .= " -r $resolution";
+	}
+	$output = rrdtool_execute($cmd_line, false, RRDTOOL_OUTPUT_STDOUT);
 
 	/* grab the first line of the output which contains a list of data sources
 	in this .rrd file */