Camera matrix drastically change between successive calibrations of a low resolution camera

edit

I'm using camera_calibration package to calibrate a camera using checkerboard (in gazebo environment). The resolution of the camera is 84x84, and I've managed to calibrate the camera thrice.

camera matrix
18.869876 0.000000   42.232541
0.000000   18.817910 46.843425
0.000000   0.000000   1.000000

projection
19.568193       0.000000       41.369775   0.000000
0.000000         19.412340     45.832273   0.000000
0.000000         0.000000       1.000000     0.000000

distortion
-0.003044 0.000774 -0.000227 -0.001105 0.0000



camera matrix
59.194174 0.000000   41.422579
0.000000   59.220697 43.212139
0.000000   0.000000   1.000000

projection
58.686417       0.000000       40.837182   0.000000
0.000000         58.767673     42.702490   0.000000
0.000000         0.000000       1.000000     0.000000

distortion
-0.004351 0.007664 0.000151 -0.000845 0.0000



camera matrix
46.885763 0.000000   41.564895
0.000000   46.850151 41.490714
0.000000   0.000000   1.000000

projection
46.414661       0.000000       41.097325   0.000000
0.000000         46.358101     41.072972   0.000000
0.000000         0.000000       1.000000     0.000000

distortion
0.002144 -0.001044 0.000596 0.000203 0.0000

I'd also like to add that all 'X', 'Y', 'scale' and 'skew' bars were not green.

Calibration window: https://drive.google.com/open?id=1_Di... Gazebo env.: https://drive.google.com/open?id=1v03...