diff --git a/SGDP4.cpp b/SGDP4.cpp
index 625c5e5..d26527f 100644
--- a/SGDP4.cpp
+++ b/SGDP4.cpp
@@ -247,15 +247,15 @@ void SGDP4::FindPosition(double tsince) {
     } else {
         double xmp = xmdf;
         if (!i_use_simple_model_) {
-            double delomg = omgcof_ * tsince;
-            double delm = xmcof_ * (pow(1.0 + i_eta_ * cos(xmdf), 3.0) - delmo_);
+            double delomg = i_omgcof_ * tsince;
+            double delm = i_xmcof_ * (pow(1.0 + i_eta_ * cos(xmdf), 3.0) - i_delmo_);
             double temp1 = delomg + delm;
             xmp = xmdf + temp1;
             tsince_arg_perigee -= temp1;
             double tcube = tsq * tsince;
             double tfour = tsince * tcube;
             tempa -= i_d2_ * tsq - i_d3_ * tcube - i_d4_ * tfour;
-            tempe += BStar() * i_c5_ * (sin(xmp) - sinmo_);
+            tempe += BStar() * i_c5_ * (sin(xmp) - i_sinmo_);
             templ += i_t3cof_ * tcube + tfour * (i_t4cof_ + tsince * i_t5cof_);
         }
         a = RecoveredSemiMajorAxis() * pow(tempa, 2.0);
diff --git a/SGDP4.h b/SGDP4.h
index 9ed7115..3721709 100644
--- a/SGDP4.h
+++ b/SGDP4.h
@@ -23,7 +23,7 @@ private:
     bool first_run_;
 
     /*
-     * i_ variables are constants that wont be modified outside Init
+     * variables are constants that wont be modified outside init
      */
     double i_cosio_;
     double i_sinio_;
@@ -33,7 +33,6 @@ private:
     double i_a3ovk2_;
     double i_x1mth2_;
     double i_c4_;
-    double i_c5_;
     double i_xmdot_;
     double i_omgdot_;
     double i_xnodot_;
@@ -42,6 +41,10 @@ private:
     double i_xlcof_;
     double i_aycof_;
     double i_x7thm1_;
+    /*
+     * sgp4 constant
+     */
+    double i_c5_;
     double i_omgcof_;
     double i_xmcof_;
     double i_delmo_;
@@ -52,6 +55,9 @@ private:
     double i_t3cof_;
     double i_t4cof_;
     double i_t5cof_;
+    /*
+     * sdp4 constant
+     */
     double i_gsto_;
 
     bool i_use_simple_model_;