Problem in understanding HC-SR04 Ultrasonic Sensor

Is it necessary to feed 10 microsecond High to Low pulse to trig pin of HC-SR04 ultrasonic sensor. I have tried I have tried less than 10 and more than 10 microseconds pulse and they also work fine for me. Every datasheet that i read says we have to feed aleast 10 microseconds TTL pulse to HC-SR04. So i don't understand whats the point in 10 microseconds if it works in other conditions as well.

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All of the data sheets that I have seen say trigger pulse width is 10us minimum. It may work with a narrower pulse but it is out of specification. The device is actually triggered on the negative edge (transition) so as long as the width meets the minmum, the unit should work.