Log/monitor distance travelled by linear track axis

In order to be able to perform some automatic service on a linear track, we would like to log the distance travelled by the 7th axis. I was wondering if there is a system variable similar to $SCR_GRP[1].$MOVE_DST that monitors movements (including jogging) of individual axes instead of the TCP point?

I have thought about running a karel program that periodically updates the current JPOS, but I would prefer not to be dependent on something like auto_exec programs if I don't have to.

Any other suggestions/ideas are welcomed as well

Thank you, that is exactly what I need! Posting my solution here (with excessive use of registers to demonstrate the method), should anyone else need something like this:

   1:  !Grab current joint position ;
   2:  R[12:current joint]=$SCR_GRP[1].$MCH_ANG[7] ;
   3:   ;
   4:  !Compute joint movement ;
   5:  IF (R[12:current joint]>R[13:previous joint]) THEN ;
   6:  R[14:distance step]=R[12:current joint]-R[13:previous joint]    ;
   7:  ELSE ;
   8:  R[14:distance step]=R[13:previous joint]-R[12:current joint]    ;
   9:  ENDIF ;
  10:   ;
  11:  !Add step to total movement ;
  12:  R[15:total distance]=R[15:total distance]+R[14:distance step]    ;
  13:   ;
  14:  !Update for next step ;
  15:  R[13:previous joint]=R[12:current joint]    ;

Note that there is a lot to optimise in terms of computation time for BG-logic, but I didn't spend any attention to this since I won't be running this in the guaranteed 8 ms cycle. Even a 1s cycle would provide more than enough resolution.