diff --git a/Data_and_operation/Number.java b/Data_and_operation/Number.java
index 2055957..e0ca07a 100644
--- a/Data_and_operation/Number.java
+++ b/Data_and_operation/Number.java
@@ -9,7 +9,13 @@ public static void main(String[] args) {
 		System.out.println(6 / 2); // 3
 
 		System.out.println(Math.PI); // 3.141592653589793
-		System.out.println(Math.floor(Math.PI));
+		
+		// floor = remove decimal point
+		// 3.141592653589793 -> 3.0 print
+		System.out.println(Math.floor(Math.PI));	
+		
+		// ceil = a decimal ascent
+		// 3.141592653589793 -> 4.0 print
 		System.out.println(Math.ceil(Math.PI));
 		
 		
diff --git a/HelloWorld_IOT/HelloWorldRaspberryPi.java b/HelloWorld_IOT/HelloWorldRaspberryPi.java
index c159e76..1d79d98 100644
--- a/HelloWorld_IOT/HelloWorldRaspberryPi.java
+++ b/HelloWorld_IOT/HelloWorldRaspberryPi.java
@@ -16,9 +16,9 @@ public static void main(String[] args) throws InterruptedException {
 
 		while (true) {
 			// H
-			pin.high();
-			Thread.sleep(SHORT_INTERVAL);
-			pin.low();
+			pin.high();						// pin LED ON
+			Thread.sleep(SHORT_INTERVAL);	// 0.2 Seconds Stop
+			pin.low();						// pin LED OFF
 			Thread.sleep(SHORT_INTERVAL);
 			pin.high();
 			Thread.sleep(SHORT_INTERVAL);