diff --git a/sentinel-core/src/main/java/com/alibaba/csp/sentinel/node/StatisticNode.java b/sentinel-core/src/main/java/com/alibaba/csp/sentinel/node/StatisticNode.java
index fa559868..43cc0039 100755
--- a/sentinel-core/src/main/java/com/alibaba/csp/sentinel/node/StatisticNode.java
+++ b/sentinel-core/src/main/java/com/alibaba/csp/sentinel/node/StatisticNode.java
@@ -44,10 +44,10 @@ import com.alibaba.csp.sentinel.slots.statistic.metric.Metric;
  * incoming request(QPS), block request(bq), etc. And the time-span is defined by sample count.
  * </p>
  * <pre>
- * 	0 	   100ms
+ * 	0      100ms
  *  +-------+--→ Sliding Windows
- * 		^
- * 	   	|
+ * 	    ^
+ * 	    |
  * 	  request
  * </pre>
  * <p>
@@ -58,29 +58,29 @@ import com.alibaba.csp.sentinel.slots.statistic.metric.Metric;
  *
  * <p>case 2: continuous requests</p>
  * <pre>
- *  0 	 100ms 	  200ms	  300ms
+ *  0    100ms    200ms    300ms
  *  +-------+-------+-------+-----→ Sliding Windows
- * 						^
- * 						|
- * 					  request
+ *                      ^
+ *                      |
+ *                   request
  * </pre>
  *
  * <p>case 3: requests keeps coming, and previous buckets become invalid</p>
  * <pre>
- *  0 	 100ms 	  200ms	  800ms	   900ms  1000ms	1300ms
+ *  0    100ms    200ms	  800ms	   900ms  1000ms    1300ms
  *  +-------+-------+ ...... +-------+-------+ ...... +-------+-----→ Sliding Windows
- *  													^
- *  													|
- * 													  request
+ *                                                      ^
+ *                                                      |
+ *                                                    request
  * </pre>
  *
  * <p>The sliding window should become:</p>
  * <pre>
- * 300ms	  	800ms  900ms  1000ms	1300ms
+ * 300ms     800ms  900ms  1000ms  1300ms
  *  + ...... +-------+ ...... +-------+-----→ Sliding Windows
- *  													^
- *  													|
- * 													  request
+ *                                                      ^
+ *                                                      |
+ *                                                    request
  * </pre>
  *
  * @author qinan.qn
diff --git a/sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/statistic/StatisticSlot.java b/sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/statistic/StatisticSlot.java
index 67ddc4a9..8a6c3779 100755
--- a/sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/statistic/StatisticSlot.java
+++ b/sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/statistic/StatisticSlot.java
@@ -35,10 +35,10 @@ import com.alibaba.csp.sentinel.slots.block.BlockException;
  * When entering this slot, we need to separately count the following
  * information:
  * <ul>
- * <li>{@link ClusterNode}: total statistics of a cluster node of the resource id  </li>
- * <li> origin node: statistics of a cluster node from different callers/origins.</li>
- * <li> {@link DefaultNode}: statistics for specific resource name in the specific context.
- * <li> Finally, the sum statistics of all entrances.</li>
+ * <li>{@link ClusterNode}: total statistics of a cluster node of the resource ID.</li>
+ * <li>Origin node: statistics of a cluster node from different callers/origins.</li>
+ * <li>{@link DefaultNode}: statistics for specific resource name in the specific context.</li>
+ * <li>Finally, the sum statistics of all entrances.</li>
  * </ul>
  * </p>
  *
@@ -51,24 +51,31 @@ public class StatisticSlot extends AbstractLinkedProcessorSlot<DefaultNode> {
     public void entry(Context context, ResourceWrapper resourceWrapper, DefaultNode node, int count, Object... args)
         throws Throwable {
         try {
+            // Do some checking.
             fireEntry(context, resourceWrapper, node, count, args);
+
+            // Request passed, add thread count and pass count.
             node.increaseThreadNum();
             node.addPassRequest();
 
             if (context.getCurEntry().getOriginNode() != null) {
+                // Add count for origin node.
                 context.getCurEntry().getOriginNode().increaseThreadNum();
                 context.getCurEntry().getOriginNode().addPassRequest();
             }
 
             if (resourceWrapper.getType() == EntryType.IN) {
+                // Add count for global inbound entry node for global statistics.
                 Constants.ENTRY_NODE.increaseThreadNum();
                 Constants.ENTRY_NODE.addPassRequest();
             }
 
+            // Handle pass event with registered entry callback handlers.
             for (ProcessorSlotEntryCallback<DefaultNode> handler : StatisticSlotCallbackRegistry.getEntryCallbacks()) {
                 handler.onPass(context, resourceWrapper, node, count, args);
             }
         } catch (BlockException e) {
+            // Blocked, set block exception to current entry.
             context.getCurEntry().setError(e);
 
             // Add block count.
@@ -78,18 +85,21 @@ public class StatisticSlot extends AbstractLinkedProcessorSlot<DefaultNode> {
             }
 
             if (resourceWrapper.getType() == EntryType.IN) {
+                // Add count for global inbound entry node for global statistics.
                 Constants.ENTRY_NODE.increaseBlockQps();
             }
 
+            // Handle block event with registered entry callback handlers.
             for (ProcessorSlotEntryCallback<DefaultNode> handler : StatisticSlotCallbackRegistry.getEntryCallbacks()) {
                 handler.onBlocked(e, context, resourceWrapper, node, count, args);
             }
 
             throw e;
         } catch (Throwable e) {
+            // Unexpected error, set error to current entry.
             context.getCurEntry().setError(e);
 
-            // Should not happen
+            // This should not happen.
             node.increaseExceptionQps();
             if (context.getCurEntry().getOriginNode() != null) {
                 context.getCurEntry().getOriginNode().increaseExceptionQps();
@@ -107,11 +117,13 @@ public class StatisticSlot extends AbstractLinkedProcessorSlot<DefaultNode> {
         DefaultNode node = (DefaultNode)context.getCurNode();
 
         if (context.getCurEntry().getError() == null) {
+            // Calculate response time (max RT is TIME_DROP_VALVE).
             long rt = TimeUtil.currentTimeMillis() - context.getCurEntry().getCreateTime();
             if (rt > Constants.TIME_DROP_VALVE) {
                 rt = Constants.TIME_DROP_VALVE;
             }
 
+            // Record response time and success count.
             node.rt(rt);
             if (context.getCurEntry().getOriginNode() != null) {
                 context.getCurEntry().getOriginNode().rt(rt);
@@ -131,6 +143,7 @@ public class StatisticSlot extends AbstractLinkedProcessorSlot<DefaultNode> {
             // Error may happen.
         }
 
+        // Handle exit event with registered exit callback handlers.
         Collection<ProcessorSlotExitCallback> exitCallbacks = StatisticSlotCallbackRegistry.getExitCallbacks();
         for (ProcessorSlotExitCallback handler : exitCallbacks) {
             handler.onExit(context, resourceWrapper, count, args);