Due to problems with lasers during Run XIII (especially in May) I tried to estimate drift velocity from membrane clusters.
Below there is a plot for laser runs with successful drift velocity estimations (dvAll with respect to drift velocity which has been in DB before (vWest)) where drift velocity has beed estimated using the standard techniques from laser beams pointing 
to a mirror versus sum east and west drift distances of membrane clusters
 

Using the above parameterization estimations of drift velocities have been plot below

and the same plot for May only

From the above plot I see that a reasonable estimation (i.e. better than nothing) can be done using membrane cluser positions.
The correction to LoopOverLaserTrees.C macro has been done and the macro has been put in CVS.