But there seems to be change in the virtual image position of the device whenever I open it. What is the procedure to make this virtual image location fix ? Does it cause any problem for the reading of data ?
This is a not a cause for concern. Each time you load the initial setup program, the virtual image position open’s at it’s default position even if it has been ran before at a different position.
Sometimes it is 30hz, 27hz and 25hz etc. but never above 40Hz. Why is the sampling rate different for my device ? Do i need to do some calibration ?
There is to be expected a variation around the nominal value of ~55Hz however that you mention there is no sampling higher than 40Hz is not normal behaviour. You may have already read the article discussing the variable sample rate of the EyeX @ https://link.springer.com/article/10.3758/s13428-016-0762-9
It would be helpful if you gathered a larger sample size and kindly informed us of your methodology to determine the sample frequency. If possible to test with another user as well and report back. Thanks.