diff --git a/src/Classic/AbsBeamline/Monitor.cpp b/src/Classic/AbsBeamline/Monitor.cpp
index 442bf9ecaea260fd9a325c54eb05105dbf048c85..71aac8a96336007e93bd490f653396a141cd3f6a 100644
--- a/src/Classic/AbsBeamline/Monitor.cpp
+++ b/src/Classic/AbsBeamline/Monitor.cpp
@@ -74,15 +74,17 @@ bool Monitor::apply(const size_t &i, const double &t, Vector_t &/*E*/, Vector_t
     const Vector_t &R = RefPartBunch_m->R[i];
     const Vector_t &P = RefPartBunch_m->P[i];
     const double &dt = RefPartBunch_m->dt[i];
-    const double recpgamma = Physics::c * dt / Util::getGamma(P);
-    const double middle = 0.5 * getElementLength();
+    const Vector_t singleStep  = Physics::c * dt * Util::getBeta(P);
     if (online_m && type_m == SPATIAL) {
-        if (dt * R(2) < dt * middle && // multiply with dt to allow back tracking
-            dt * (R(2) + P(2) * recpgamma) > dt * middle) {
-            double frac = (middle - R(2)) / (P(2) * recpgamma);
-
-            lossDs_m->addParticle(R + frac * recpgamma * P,
-                                  P, RefPartBunch_m->ID[i], t + frac * dt, 0);
+        if (dt * R(2) < 0.0 &&
+            dt * (R(2) + singleStep(2)) > 0.0) {
+            double frac = R(2) / singleStep(2);
+
+            lossDs_m->addParticle(R + frac * singleStep,
+                                  P,
+                                  RefPartBunch_m->ID[i],
+                                  t + frac * dt,
+                                  0);
         }
     }
 
@@ -96,15 +98,15 @@ bool Monitor::applyToReferenceParticle(const Vector_t &R,
                                        Vector_t &) {
     if (!OpalData::getInstance()->isInPrepState()) {
         const double dt = RefPartBunch_m->getdT();
-        const double recpgamma = Physics::c * dt / Util::getGamma(P);
-        const double middle = 0.5 * getElementLength();
+        const double cdt = Physics::c * dt;
+        const Vector_t singleStep = cdt * Util::getBeta(P);
 
-        if (dt * R(2) < dt * middle && // multiply with dt to allow back tracking
-            dt * (R(2) + P(2) * recpgamma) > dt * middle) {
-            double frac = (middle - R(2)) / (P(2) * recpgamma);
+        if (dt * R(2) < 0.0 &&
+            dt * (R(2) + singleStep(2)) > 0.0) {
+            double frac = -R(2) / singleStep(2);
             double time = t + frac * dt;
-            Vector_t dR = (0.5 + frac) * P * recpgamma;
-            double ds = euclidean_norm(dR);
+            Vector_t dR = frac * singleStep;
+            double ds = euclidean_norm(dR + 0.5 * singleStep);
             lossDs_m->addReferenceParticle(csTrafoGlobal2Local_m.transformFrom(R + dR),
                                            csTrafoGlobal2Local_m.rotateFrom(P),
                                            time,
@@ -115,10 +117,13 @@ bool Monitor::applyToReferenceParticle(const Vector_t &R,
                 const unsigned int localNum = RefPartBunch_m->getLocalNum();
 
                 for (unsigned int i = 0; i < localNum; ++ i) {
-                    const double recpgamma = Physics::c * dt / Util::getGamma(RefPartBunch_m->P[i]);
-                    lossDs_m->addParticle(RefPartBunch_m->R[i] + frac * RefPartBunch_m->P[i] * recpgamma - halfLength_s,
-                                          RefPartBunch_m->P[i], RefPartBunch_m->ID[i],
-                                          time, 0);
+                    Vector_t shift = ((frac - 0.5) * cdt * Util::getBeta(RefPartBunch_m->P[i])
+                                      - singleStep);
+                    lossDs_m->addParticle(RefPartBunch_m->R[i] + shift,
+                                          RefPartBunch_m->P[i],
+                                          RefPartBunch_m->ID[i],
+                                          time,
+                                          0);
                 }
                 OpalData::OPENMODE openMode;
                 if (numPassages_m > 0) {
diff --git a/src/Classic/AbsBeamline/Monitor.h b/src/Classic/AbsBeamline/Monitor.h
index 16cffa89dbe8576dd668516467519139f059f2db..81231d1c6dc97c3fb5dee4c92f682c3cf2989fb8 100644
--- a/src/Classic/AbsBeamline/Monitor.h
+++ b/src/Classic/AbsBeamline/Monitor.h
@@ -105,6 +105,8 @@ public:
     void setType(Type type);
 
     static void writeStatistics();
+
+    virtual bool isInside(const Vector_t &r) const override;
 private:
 
     // Not implemented.
@@ -125,4 +127,11 @@ void Monitor::setType(Monitor::Type type) {
     type_m = type;
 }
 
-#endif // CLASSIC_Monitor_HH
\ No newline at end of file
+inline
+bool Monitor::isInside(const Vector_t &r) const
+{
+    const double length = getElementLength();
+    return std::abs(r(2)) <= 0.5 * length && isInsideTransverse(r);
+}
+
+#endif // CLASSIC_Monitor_HH
diff --git a/src/Classic/Utilities/Util.h b/src/Classic/Utilities/Util.h
index 42479de4b024055ced8e0e5cc28a80a702a933e2..44816c5a14fb74d097b343aeeea91d2952c61930 100644
--- a/src/Classic/Utilities/Util.h
+++ b/src/Classic/Utilities/Util.h
@@ -28,6 +28,11 @@ namespace Util {
         return std::sqrt(dot(p, p) + 1.0);
     }
 
+    inline
+    Vector_t getBeta(Vector_t p) {
+        return p / getGamma(p);
+    }
+
     inline
     double getKineticEnergy(Vector_t p, double mass) {
         return (getGamma(p) - 1.0) * mass;
@@ -45,7 +50,7 @@ namespace Util {
     double convertMomentumeVToBetaGamma(double p, double mass) {
         return p / mass;
     }
-  
+
     inline
     std::string getTimeString(double time, unsigned int precision = 3) {
         std::string timeUnit(" [ps]");
@@ -170,7 +175,7 @@ namespace Util {
     }
 
     Vector_t getTaitBryantAngles(Quaternion rotation, const std::string &elementName = "");
-  
+
     std::string toUpper(const std::string &str);
 
     std::string combineFilePath(std::initializer_list<std::string>);
diff --git a/src/Elements/OpalBeamline.cpp b/src/Elements/OpalBeamline.cpp
index 054b74f2d82ed73e26a8fdf7bfb3d0eec7626b59..d57d1cd6774f8eab9a414219204dcf18d341701a 100644
--- a/src/Elements/OpalBeamline.cpp
+++ b/src/Elements/OpalBeamline.cpp
@@ -322,9 +322,6 @@ void OpalBeamline::compute3DLattice() {
         if (element->getType() == ElementBase::SOURCE) {
             beginThis3D(2) -= thisLength;
         }
-        if (element->getType() == ElementBase::MONITOR) {
-            beginThis3D(2) -= 0.5 * thisLength;
-        }
 
         Vector_t endThis3D;
         if (element->getType() == ElementBase::SBEND ||