What's "pose_left.txt" in KITTI dataset, Visual Odometry?

I notice there's a pose_left.txt in the KITTI_VO dataset, which has 7 number each row like:

2.220445999999999902e-16 1.665335000000000021e-16 -1.110222999999999951e-16 0.000000000000000000e+00 0.000000000000000000e+00 0.000000000000000000e+00 1.000000000000000000e+00
6.068196999999999619e+00 8.752694999999999226e+00 3.367873000000000117e-01 1.580063374987697097e-02 -1.842944918288907941e-02 5.972132198910096168e-01 8.017150774204823138e-01
6.260272999999999755e+00 9.421853000000000478e+00 3.626882000000000161e-01 1.590135731782738732e-02 -1.971411599043487034e-02 6.016278338303453488e-01 7.983748806336361525e-01

I'm guessing it's the transformation parameters, but there should be 6: translation(3) and rotation(3). Why should there be an extra one?