why iam getting inconsistent ultraonic sensor readings for the HC-SRO4

hullo have tried several ultrasonic code using basic code of pulseln() function , tried new ping library iam still getting erroneous distances readings.
whether put obstacle or not, still these sets of results. iam desperate advice or might problem. hc-sro4 sensors or confined in room.
the results below using new ping library
 https://bitbucket.org/teckel12/arduino-new-ping/wiki/home#!issue-tracking

ping: 0cm
ping: 129cm
ping: 128cm
ping: 127cm
ping: 127cm
ping: 129cm
ping: 129cm

then when not using library pulseln() function calculate duration before calculate distance of sound.

code: [select]

digitalwrite(trigpin, low); //clear trigpin
     delaymicroseconds(2);
     digitalwrite(trigpin, high);
     digitalwrite(trigpin, low);
     //once received echo calculate distance duration
     duration = pulsein(echopin, high);
     distance = (duration/2)/29.1 ; //distance in inches..
     //distance = duration/58.2;  ////calculate distance (in cm) based on speed of sound.
     delay(300); //for stability  used 300
these results.
distance: 123
distance: 123
distance: 123
distance: 122
distance: 122
distance: 124
distance: 124

i have had no problems newping library.

- sure wires device ok? worth swapping them dfferent set try.
- have got sensor try hardware problem

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