What Is the Length?

#include <SR04.h>

/*
 * ElegooHC-SR501-01.ino
 * Measure distance using the HC-SR504 ultrasonic sensor
 * adapted from examples at https://www.elegoo.com/
 * 2018-09-12
 * armw
 * v0.1
 * � 2018 <reza@parkcircus.org> All Rights Reserved
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA 02110-1301, USA.
 * 
 * Notes
 *   HC-SR504:
 *     Pin #  Description
 *     1      VCC
 *     2      Trigger
 *     3      Echo
 *     4      GND
 *   Datasheet: http://elecfreaks.com/estore/download/EF03085-HC-SR04_Ultrasonic_Module_User_Guide.pdf
 *   Distance = Ultrasonic (air) velocity * EchoDetectionTime/2
 */

#define pinTrig 6                 // pin to initiate transmission of sound pulse
#define pinEcho 7                 // pin to receive the signal of echo from the sound pulse
#define blinkPeriod 1000          // nominal delay between discrete activities, microseconds

SR04 mySensor = SR04(pinEcho, pinTrig); // instatiation of object to retain sensor data

void setup()                        // run only once
{
  Serial.begin(115200);             // default initialize of serial port that will be used to display distance readout
  delay(blinkPeriod);               // wait for 1,000 microseconds
  Serial.println("HC-SR504 simple test using Elegoo SR04 library.");
}

void loop()                         // run indefinitely
{
  int myDistance = mySensor.Distance(); // obtain estimated distance using pulse/echo signals
  Serial.print("Distance = ");
  Serial.print(myDistance);
  Serial.print(" cm, = ");
  myDistance = 0.3937008 * myDistance; // convert from centimeters to inches
  Serial.print(myDistance);
  Serial.println(" in");
  delay(blinkPeriod);               // pause
}