update readme

README.md

@@ -23,7 +23,9 @@ void setup() {
 
 void loop() {
     if (mpu.update()) {
-        mpu.printRollPitchYaw();
+        Serial.print(mpu.getYaw()); Serial.print(", ");
+        Serial.print(mpu.getPitch()); Serial.print(", ");
+        Serial.println(mpu.getRoll());
     }
 }
 ```
@@ -53,13 +55,15 @@ void setup() {
     // calibrate anytime you want to
     mpu.calibrateAccelGyro();
     mpu.calibrateMag();
-
-    mpu.printCalibration();
 }
 
 void loop() { }
 ```
 
+### Coordinate
+
+The coordinate of quaternion and euler angles are based on the axes of acceleration and gyro sensors (Right-Handed, X-forward, Z-up). On the other hand, roll, pitch, and yaw angles are basedd on airplane coordinate (Right-Handed, X-forward, Z-down). Please use `getEulerX/Y/Z()` for euler angles and `getRoll/Pitch/Yaw()` for airplane coordinate angles.
+
 
 ## Other Settings
 
@@ -189,7 +193,6 @@ MPU9255 mpu;
 bool setup(const uint8_t addr, const MPU9250Setting& setting, WireType& w = Wire);
 void verbose(const bool b);
 void ahrs(const bool b);
-void useRawPitchYawRollDirection(const bool b);
 void calibrateAccelGyro();
 void calibrateMag();
 bool isConnected();
@@ -202,7 +205,10 @@ float getRoll() const;
 float getPitch() const;
 float getYaw() const;
 
-float getQuaternion(uint8_t i) const;
+float getEulerX() const;
+float getEulerY() const;
+float getEulerZ() const;
+
 float getQuaternionX() const;
 float getQuaternionY() const;
 float getQuaternionZ() const;
@@ -253,15 +259,6 @@ void setMagScale(const float x, const float y, const float z);
 void setMagneticDeclination(const float d);
 
 bool selftest();
-
-void print() const;
-void printRawData() const;
-void printAcc() const;
-void printGyro() const;
-void printMag() const;
-void printQuaternion() const;
-void printRollPitchYaw() const;
-void printCalibration() const;
 ```
 
 ## License