--- a/main.c	Wed Jun 13 23:41:05 2012 +0800
+++ b/main.c	Thu Jun 14 00:00:57 2012 +0800
@@ -262,7 +262,7 @@
 cmd_clear()
 {
     n_measurements = 0;
-    printf_P(PSTR("Cleared\n"));
+    printf_P(PSTR("cleared\n"));
 }
 
 static void

--- a/server/ts.py	Wed Jun 13 23:41:05 2012 +0800
+++ b/server/ts.py	Thu Jun 14 00:00:57 2012 +0800
@@ -109,13 +109,28 @@
 
     return int(next_wake)
 
+@retry()
+def clear_meas(sock):
+    sock.send("clear\n");
+    l = readline(sock)
+    if l and l.rstrip() == 'cleared':
+        return True
+
+    print>>sys.stderr, "Bad response to clear %s\n" % str(l)
+    return False
+
 def send_results(lines):
     enc_lines = binascii.b2a_base64(zlib.compress('\n'.join(lines)))
     hmac.new(config.HMAC_KEY, enc_lines).hexdigest()
 
     url_data = urllib.url_encode( ('lines', enc_lines), ('hmac', mac) )
     con = urllib2.urlopen(config.UPDATE_URL, url_data)
-
+    result = con.read(100)
+    if result == 'OK':
+        return True
+    else:
+        print>>sys.stderr, "Bad result '%s'" % result
+        return False
 
 def do_comms(sock):
     print "do_comms"

--- a/web/log.py	Wed Jun 13 23:41:05 2012 +0800
+++ b/web/log.py	Thu Jun 14 00:00:57 2012 +0800
@@ -71,7 +71,10 @@
         zip((first_real_time + time_step*t for t in xrange(len(measurements))),
             measurements)]
 
-    rrdtool.update(sensor_rrd_path(sensor_id), *values)
+    rrdfile = sensor_rrd_path(sensor_id)
+    rrdtool.update(rrdfile, *values)
+    f = file(rrdfile)
+    os.fsync(f.fileno())
 
 def parse(lines):
     entries = dict(l.split('=', 1) for l in lines)