diff --git a/tracy/tracy/inc/tracy_global.h b/tracy/tracy/inc/tracy_global.h
index b044732c2e71a856519353573af98d50f0254765..d9d33e020a881c61ee135078ca58ee3e41866ff1 100644
--- a/tracy/tracy/inc/tracy_global.h
+++ b/tracy/tracy/inc/tracy_global.h
@@ -88,14 +88,14 @@ struct MpoleType {
   double      PdTrms;    // rms [deg]
   double      PdTrnd;    // random error??? [deg]
   // Multipole strengths
-  mpolArray   PBpar;     // design
+  mpolArray   PBpar;     // design field strength
   mpolArray   PBsys;     // systematic multipole errors
   mpolArray   PBrms;     // rms multipole field errors
-  mpolArray   PBrnd;     // random number, random error?????
-  mpolArray   PB;        // total field strength
+  mpolArray   PBrnd;     // random scale factor of rms error PBrms
+  mpolArray   PB;        // total field strength(design,sys,rms)
   int         Porder;    // The highest order in PB
   int         n_design;  // multipole order (design)
-  pthicktype  Pthick;
+  pthicktype  Pthick;    // thick element
   // Bending Angles
   double PTx1;           // horizontal entrance angle [deg]
   double PTx2;           // horizontal exit angle [deg]
@@ -125,8 +125,8 @@ struct WigglerType {
   int    harm[n_harm_max];    // harmonic number
   double BoBrhoV[n_harm_max]; // B/Brho vertical
   double BoBrhoH[n_harm_max]; // B/Brho horizontal 
-  double kxV[n_harm_max];     // kx 
-  double kxH[n_harm_max];     // kx 
+  double kxV[n_harm_max];     // vertical kx 
+  double kxH[n_harm_max];     // horizontal kx 
   double phi[n_harm_max];     // phi 
   mpolArray PBW;
   Matrix W55;                 // Transport matrix 
diff --git a/tracy/tracy/src/t2elem.cc b/tracy/tracy/src/t2elem.cc
index 26be9933a1c685e6e777f68d90c3b3ab6763f0ed..9668de70f0b7b17e3673a342970d8f30168ce262 100644
--- a/tracy/tracy/src/t2elem.cc
+++ b/tracy/tracy/src/t2elem.cc
@@ -3907,7 +3907,8 @@ void Solenoid_Init(int Fnum1) {
  Purpose:
  called by Cell_SetdP
  Compute full multipole composent as sum of design, systematic
- and random part
+ and random part.
+ The ramdom error is the multiplication of PBrms and PBrnd
  Compute transport matrix if quadrupole (Order=2)
  Set multipole order to Order if multipole (Order >2)