When the annotation function (Pen icon from the float bar) is being used it's possible that your calibration is slightly offset (around an inch). To correct this, please adjust the settings of your browser by following the steps below:
Click on the hamburger menu in your browser's right top corner, and choose Settings.
Now select the Display Settings
Please check the 'hide status bar while browsing'
After restarting the browser the calibration will be spot on!