Incorrect Distance Readings from HC-SR04 Ultrasonic Sensor on BeagleBone Black

def measure_distance_simple():
    GPIO.output(TRIG_PIN, GPIO.HIGH)
    time.sleep(0.00001)
    GPIO.output(TRIG_PIN, GPIO.LOW)

    while GPIO.input(ECHO_PIN) == GPIO.LOW:
        start_time = time.time()

    while GPIO.input(ECHO_PIN) == GPIO.HIGH:
        end_time = time.time()

    duration = end_time - start_time
    distance = (duration * 34300) / 2
    return distance

try:
    while True:
        distance = measure_distance_simple()
        print(f"Distance: {distance:.2f} cm")
        time.sleep(1)

except KeyboardInterrupt:
    GPIO.cleanup()