ETA is only as good as the data we give it, therefor if we have inconsistent clocking and flagging of labor to techs then our data will reflect that. Typically by looking at the data we can figure out where the problem is, i.e. if the RO/Flagged labor hours are drastically lower than clocked hours is indicitive of incorrect labor flagging. The reverse is also true where Flagged Labor hours are high and clocked hours are very low this would indicate we are not clocking into RO's with Tech Central or SuMo.
If you're a shop that doesn't flag labor but does record time clock RO punches you may want to check out Tech Metrix which calculates a cost based efficiency based on timeclock punches.