Test results different in API and browser executed tests

I have installed the private instance and i am able to run the tests using a web browser. For ex:

  1. I open http://myprivateinstance.webpagetest.com

  2. Enter the URL to be tested and then click on submit. I see some test results

  3. Now i execute(Have the node wrapper installed):
    #webpatetest test http://urltobetested.com -s myprivateinstance.webpagetest.com > testresults.txt

  4. Fetch the JSON URL from test results, parse it and fetch the FirstByte, Loadtime, FullyLoaded time etc.

  5. The test results vary by approximately 2 Seconds when compared to the test results generated on a browser in step 2 above. I fetch the median values from the JSON.

Why is there a significant difference in test results? Am i missing on some thing.

Had to recheck my settings. I have confidence in the consistent metrics now.