The unit used in the translation vector (T matrix) is the same unit used when you specify the object coordinate points. Without knowing more about your calibration setup, its hard to say why you don't see meaningful values. Some things to consider would be:
- Make sure your object point coordinates are correct and match up to the detected image points
- Verify the reproduction error. The error should be below one pixel is the calibration is good
- Make sure the left and right image pairs correspond. Also make the board was detected in each image with the same orientation. With symmetrical boards it can sometimes happen that the detected board layout flips between the left and right view.
- Ensure that your image capture of both cameras is synchronised. This is more challenging than it initially seems. If your calibration scene is not static, i.e. your are manually holding the board or the cameras, and you are not having synchronised capture you can easily get motion between the two corresponding images. This can greatly distort your extrinsic calibration results.
