diff --git a/ntp_core.c b/ntp_core.c
index a198545..af47516 100644
--- a/ntp_core.c
+++ b/ntp_core.c
@@ -1325,6 +1325,43 @@ check_packet_auth(NTP_Packet *pkt, int length,
 
 /* ================================================== */
 
+static int
+check_delay_dev_ratio(NCR_Instance inst, SST_Stats stats,
+                      struct timespec *sample_time, double offset, double delay)
+{
+  double last_sample_ago, predicted_offset, min_delay, skew, std_dev;
+  double delta, max_delta, error_in_estimate;
+
+  if (!SST_GetDelayTestData(stats, sample_time, &last_sample_ago,
+                            &predicted_offset, &min_delay, &skew, &std_dev))
+    return 1;
+
+  /* Require that the ratio of the increase in delay from the minimum to the
+     standard deviation is less than max_delay_dev_ratio.  In the allowed
+     increase in delay include also dispersion. */
+
+  max_delta = std_dev * inst->max_delay_dev_ratio +
+              last_sample_ago * (skew + LCL_GetMaxClockError());
+  delta = (delay - min_delay) / 2.0;
+
+  if (delta <= max_delta)
+    return 1;
+
+  error_in_estimate = offset + predicted_offset;
+
+  /* Before we decide to drop the sample, make sure the difference between
+     measured offset and predicted offset is not significantly larger than
+     the increase in delay */
+  if (fabs(error_in_estimate) - delta > max_delta)
+    return 1;
+
+  DEBUG_LOG("maxdelaydevratio: error=%e delay=%e delta=%e max_delta=%e",
+            error_in_estimate, delay, delta, max_delta);
+  return 0;
+}
+
+/* ================================================== */
+
 static int
 receive_packet(NCR_Instance inst, NTP_Local_Address *local_addr,
                NTP_Local_Timestamp *rx_ts, NTP_Packet *message, int length)
@@ -1554,8 +1591,7 @@ receive_packet(NCR_Instance inst, NTP_Local_Address *local_addr,
        in the register is less than an administrator-defined value or the
        difference between measured offset and predicted offset is larger than
        the increase in delay */
-    testC = SST_IsGoodSample(stats, -offset, delay, inst->max_delay_dev_ratio,
-                             LCL_GetMaxClockError(), &sample_time);
+    testC = check_delay_dev_ratio(inst, stats, &sample_time, offset, delay);
 
     /* Test D requires that the remote peer is not synchronised to us to
        prevent a synchronisation loop */
diff --git a/sourcestats.c b/sourcestats.c
index a4a9802..cf3d813 100644
--- a/sourcestats.c
+++ b/sourcestats.c
@@ -813,39 +813,21 @@ SST_MinRoundTripDelay(SST_Stats inst)
 /* ================================================== */
 
 int
-SST_IsGoodSample(SST_Stats inst, double offset, double delay,
-    double max_delay_dev_ratio, double clock_error, struct timespec *when)
+SST_GetDelayTestData(SST_Stats inst, struct timespec *sample_time,
+                     double *last_sample_ago, double *predicted_offset,
+                     double *min_delay, double *skew, double *std_dev)
 {
-  double elapsed, allowed_increase, delay_increase;
-
   if (inst->n_samples < 6)
-    return 1;
+    return 0;
 
-  elapsed = UTI_DiffTimespecsToDouble(when, &inst->offset_time);
+  *last_sample_ago = UTI_DiffTimespecsToDouble(sample_time, &inst->offset_time);
+  *predicted_offset = inst->estimated_offset +
+                      *last_sample_ago * inst->estimated_frequency;
+  *min_delay = SST_MinRoundTripDelay(inst);
+  *skew = inst->skew;
+  *std_dev = inst->std_dev;
 
-  /* Require that the ratio of the increase in delay from the minimum to the
-     standard deviation is less than max_delay_dev_ratio. In the allowed
-     increase in delay include also skew and clock_error. */
-    
-  allowed_increase = inst->std_dev * max_delay_dev_ratio +
-    elapsed * (inst->skew + clock_error);
-  delay_increase = (delay - SST_MinRoundTripDelay(inst)) / 2.0;
-
-  if (delay_increase < allowed_increase)
-    return 1;
-
-  offset -= inst->estimated_offset + elapsed * inst->estimated_frequency;
-
-  /* Before we decide to drop the sample, make sure the difference between
-     measured offset and predicted offset is not significantly larger than
-     the increase in delay */
-  if (fabs(offset) - delay_increase > allowed_increase)
-    return 1;
-
-  DEBUG_LOG("Bad sample: offset=%f delay=%f incr_delay=%f allowed=%f",
-            offset, delay, delay_increase, allowed_increase);
-
-  return 0;
+  return 1;
 }
 
 /* ================================================== */
diff --git a/sourcestats.h b/sourcestats.h
index 9b34cc6..f0a5ca9 100644
--- a/sourcestats.h
+++ b/sourcestats.h
@@ -126,10 +126,10 @@ extern double SST_PredictOffset(SST_Stats inst, struct timespec *when);
 /* Find the minimum round trip delay in the register */
 extern double SST_MinRoundTripDelay(SST_Stats inst);
 
-/* This routine determines if a new sample is good enough that it should be
-   accumulated */
-extern int SST_IsGoodSample(SST_Stats inst, double offset, double delay,
-   double max_delay_dev_ratio, double clock_error, struct timespec *when);
+/* Get data needed for testing NTP delay */
+extern int SST_GetDelayTestData(SST_Stats inst, struct timespec *sample_time,
+                                double *last_sample_ago, double *predicted_offset,
+                                double *min_delay, double *skew, double *std_dev);
 
 extern void SST_SaveToFile(SST_Stats inst, FILE *out);