NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.7

Using Arduino Sensors
11

You've got two virtually-identical constructors; you could eliminate code by defaulting "max_cm_distance" to "MAX_SENSOR_DISTANCE", couldn't you?

int NewPing::convert_cm(int echoTime) {
	if (!echoTime) return false;
	else return echoTime / US_ROUNDTRIP_CM;
}

If "echoTime" is zero, then "echoTime / US_ROUNDTRIP_CM" is also zero; no need to test up front - slightly longer execution time, shorter code.