Data files specifying the rover's position, orientation and speed over time are updated by the NASA/JPL mission team approximately once per sol and posted to the Navigation and Ancillary Information Facility (NAIF) web site. NAIF MSL files are checked regularly by this web site and processed to create the drive log.
Drive distance is given in meters, down to centimeter accuracy per the NAIF files. The Mars time of the start of the drive is given as sol number and local mean solar time (LMST) at the rover's landing spot. The drive start time is also given in universal coordinated time (UTC), which is effectively GMT or Zulu time.
The odometer reading gives the total distance traveled by the rover in meters.
Rover orientation at the end of the drive is given as azimuth, roll and pitch, in degrees. Azimuth is defined as 0° for true north, increasing clockwise. Roll is the inclination of the angle from side to side, with 0° being level. Pitch is the inclination up or down.
Elevation, in meters, is given with respect to the landing site (Bradbury Landing).
The NAIF data files are sometimes refined after their first release, so the initial values posted may change somewhat, although usually not by a lot. The twitter notification of a particular drive/distance may thus not exactly match the distance refined after the tweet went out.
Two additional links are provided for each drive, to a map indicating the drive track in blue, and to a plot of the rover's speed vs. time during the drive.