Collect the statistics-counters needed to make the weighted average of shower axes in a cluster of several showers.
I : Shower number.
WSUM : sum of shower-axes weighted by 1/sigma^2 OOWSUM : sum of 1/sigma^2
From /ZASTE/ : IGEOM, the number of the present detector. From /ZAEVT/ : MTRK, the total number of seen particles; From /ZACLU/ : CTYPCL, calorimeter types; CLUAX, shower axis
To /ZACLU/ : PVECLU, cluster 4-momentum.
(To Check if element IN Set)