diff --git a/src/c_ggrid.cpp b/src/c_ggrid.cpp
index 46b3a42..ceb8669 100644
--- a/src/c_ggrid.cpp
+++ b/src/c_ggrid.cpp
@@ -40,19 +40,23 @@ void c_ggrid::interpolate( nec_float x, nec_float y, nec_complex *f1,
 {
     static const int nda[3] = {11,17,9}, ndpa[3] = {110, 85, 72};
 
-    bool recalculate = true;
+    /* A point below the cached region origin carries no valid index, so it
+       forces the coefficients to be rebuilt. */
+    bool jump = false;
 
-    if( (x >= m_ip_xs) && (y >= m_ip_ys) ) {
+    if( (x < m_ip_xs) || (y < m_ip_ys) ) {
+        jump = true;
+    } else {
         m_ip_ix = static_cast<int>((x - m_ip_xs) / m_ip_dx) + 1;
         m_ip_iy = static_cast<int>((y - m_ip_ys) / m_ip_dy) + 1;
-    } else {
-        /* if point lies in same 4 by 4 point region */
-        /* as previous point, old values are reused. */
-        if ( ((m_ip_ix >= m_ip_ixeg) && (m_ip_iy >= m_ip_iyeg)) &&
-             ((std::abs(m_ip_ix - m_ip_ixs) < 2) &&  (std::abs(m_ip_iy - m_ip_iys) < 2)) )
-            recalculate = false;
     }
 
+    /* if point lies in same 4 by 4 point region */
+    /* as previous point, old values are reused. */
+    bool recalculate = jump ||
+        (m_ip_ix < m_ip_ixeg) || (m_ip_iy < m_ip_iyeg) ||
+        (std::abs(m_ip_ix - m_ip_ixs) >= 2) || (std::abs(m_ip_iy - m_ip_iys) >= 2);
+
     if (true == recalculate) {
         /* determine correct grid and grid region */
         int igr;
diff --git a/src/nec_context.cpp b/src/nec_context.cpp
index e6fb98e..08e4d9e 100644
--- a/src/nec_context.cpp
+++ b/src/nec_context.cpp
@@ -2975,7 +2975,7 @@ void nec_context::efld( nec_float xi, nec_float yi, nec_float zi, nec_float ai,
   rhox= sabj* zij- salpr* yij;
   rhoy= salpr* xij- cabj* zij;
   rhoz= cabj* yij- sabj* xij;
-  rh = norm(rhox, rhoy, rhoz); // rhox* rhox+ rhoy* rhoy+ rhoz* rhoz;
+  rh = norm2(rhox, rhoy, rhoz);
   
   if ( rh <= 1.e-10) {
     xo= xi- ai* ysn;
@@ -5638,7 +5638,7 @@ void nec_context::rom2( nec_float a, nec_float b, complex_array& sum, nec_float
       WRITE(3,18)
       STOP
 */
-  int nts = 4, nx = 1;
+  int nts = 4, nx = 1, nma = 65536;
   const int n = 9;
   nec_float rx = 1e-4;
   nec_float dz = 0.0;
@@ -5666,7 +5666,7 @@ void nec_context::rom2( nec_float a, nec_float b, complex_array& sum, nec_float
   complex_array t01(9), t10(9), t20(9), t11(9);
 
   /*! tolerance for hitting upper limit */
-  const nec_float ep = _s/(1.0e4 * m_geometry->n_plus_m());
+  const nec_float ep = _s/(1.0e4 * nma);
 
   /*! upper limit */
   const nec_float zend = ze - ep;
@@ -5846,7 +5846,7 @@ C
       GO TO 5
 */
   nt=0;
-  if ( ns >= m_geometry->n_plus_m() )
+  if ( ns >= nma )
   {
     nec_error_mode em(m_output);
     m_output.string("ROM2 -- STEP SIZE LIMITED AT Z = ");
@@ -5894,7 +5894,7 @@ void nec_context::rom2( nec_float a, nec_float b, complex_array& sum, nec_float
   
   bool recalculate_fields = true;
   
-  int nts = 4, nx = 1, n = 9;
+  int nts = 4, nx = 1, n = 9, nma = 65536;
 
   /*! subinterval size */
   nec_float dz=0.0;
@@ -5918,7 +5918,7 @@ void nec_context::rom2( nec_float a, nec_float b, complex_array& sum, nec_float
   }
   
   /*! tolerance for hitting upper limit */
-  const nec_float ep = _s/(1.0e4 * m_geometry->n_plus_m());
+  const nec_float ep = _s/(1.0e4 * nma);
 
   /*! upper limit */
   const nec_float zend = ze - ep;
@@ -6015,7 +6015,7 @@ void nec_context::rom2( nec_float a, nec_float b, complex_array& sum, nec_float
     if ( tr > rx)
     {
       nt=0;
-      if ( ns <= m_geometry->n_plus_m() )
+      if ( ns <= nma )
       {
         // halve step size
         ns = ns*2;