HC-SR04 Ultrasonic ranging

Hello,
I new to the Arduino. I am trying to measure distance using the HC-SR04.
It says it is accurate to within .017 inches. My numbers are all over to the right of the decimal, For example .05 to .86.
If anyone sees anything wrong please let me know.
Thank you for any and all help,

Ken =(

// ---------------------------------------------------------------------------
// Example NewPing library sketch that does a ping about 20 times per second.
// ---------------------------------------------------------------------------

#include <NewPing.h>

#define TRIGGER_PIN 12 // Arduino pin tied to trigger pin on the ultrasonic sensor.
#define ECHO_PIN 11 // Arduino pin tied to echo pin on the ultrasonic sensor.
#define MAX_DISTANCE 500 // Maximum distance we want to ping for (in centimeters). Maximum sensor distance is rated at 400-500cm.

NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE); // NewPing setup of pins and maximum distance.

void setup() {
Serial.begin(115200); // Open serial monitor at 115200 baud to see ping results.
}

void loop() {
delay(50); // Wait 50ms between pings (about 20 pings/sec). 29ms should be the shortest delay between pings.
float uS = sonar.ping(); // Send ping, get ping time in microseconds (uS).
Serial.print(“Depth: “);
Serial.print(uS / US_ROUNDTRIP_IN); // Convert ping time to distance in cm and print result (0 = outside set distance range)
Serial.println(” inches”);
}

NewPingExampleKM.ino (1.14 KB)

..if you can within 1/2 inch. be happy! The sensor isnt that good. Soundwaves!!
google speed of sound in air wiki

.017 = 17thou, it is rated at 2 to 400 cm i.e. .79" to 157"

I can hardly believe the accuracy of this device I also have is better than half of a millimeter. There are such sonic rangers but they cost around $100. I would be convinced with 1cm accuracy using this ranger.

liudr:
I can hardly believe the accuracy of this device I also have is better than half of a millimeter. There are such sonic rangers but they cost around $100. I would be convinced with 1cm accuracy using this ranger.

What sensor are you using to get an accuracy of more than half of a millimeter.

Ken

This HC-SR04 looks identical to a Parallax Ping or the Seeedstudio jobs. They operate at 40 Khz. With a speed of sound in air of 343.2 this is a wavelength of a bit over 8.5mm. That's going to be about the best theoretical resolution you can expect. In practice and in my experience +/-25mm is a reasonable expectation.

Accuracy is another story.

Maxbotix HRLV and XL have resolution of 1mm. You can get sub-millimeter with other sensors that use 1MHz sonic waves, which have a lot shorter wave length. I have the Maxbotix sensors and I can confirm 1mm resolution. You can probably get 0.5mm by averaging.