stereoCalibrate VGA CCD camera pair

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Hi, I'm using OpenCV to calibrate a stereo pair, which are mounted on a manufactured base. The cameras are designed to be parallel. stereoCalibrate returns 0.136682 and average reprojection error 0.172633. But T=[-82.695348046976179 0.55585694118728157 -5.8423354231928650]. Why is Tz (-5.8423354231928650) of the translation vector between the coordinate systems of the cameras so big? And if I use the stereoCalibrate results to rectify the images, it seems to have an obvious rotation? Any help is greatly appreciated!