diff --git a/main.c b/main.c
index b6c052b..0cd5832 100644
--- a/main.c
+++ b/main.c
@@ -37,7 +37,6 @@
 static void apply_error_term(void);
 static void apply_error_term_at(int i);
 static void cal_interpolate(int s);
-static void transform_domain(void);
 
 void sweep(void);
 
@@ -84,7 +83,6 @@ static THD_FUNCTION(Thread1, arg)
           draw_battery_status();
       }
 
-      transform_domain();
       /* calculate trace coordinates */
       plot_into_index(measured);
       /* plot trace as raster */
@@ -119,13 +117,13 @@ transform_domain(void)
   // and calculate ifft for time domain
   float* tmp = (float*)spi_buffer;
   for (int ch = 0; ch < 2; ch++) {
-      for (int i = 0; i < 128; i++) {
+      memcpy(tmp, measured[ch], sizeof(measured[0]));
+      for (int i = 101+1; i < 128; i++) {
           tmp[i*2+0] = 0.0;
           tmp[i*2+1] = 0.0;
       }
-      memcpy(spi_buffer, measured[ch], sizeof(measured[0]));
       fft((float(*)[2])tmp, 128, 1);
-      memcpy(measured[ch], spi_buffer, sizeof(measured[0]));
+      memcpy(measured[ch], tmp, sizeof(measured[0]));
       for (int i = 0; i < 101; i++) {
           measured[ch][i][0] /= 128.0;
           measured[ch][i][1] /= 128.0;
@@ -633,11 +631,13 @@ void sweep(void)
     redraw_requested = FALSE;
     ui_process();
     if (redraw_requested)
-      return; // return to redraw screen asap.
+      break; // return to redraw screen asap.
       
     if (frequency_updated)
       goto rewind;
   }
+
+  transform_domain();
 }
 
 static void
diff --git a/plot.c b/plot.c
index 5fc7064..e3f569f 100644
--- a/plot.c
+++ b/plot.c
@@ -701,6 +701,12 @@ trace_get_info(int t, char *buf, int len)
   }
 }
 
+static float distance_of_index(int idx) {
+#define SPEED_OF_LIGHT 299792458
+   float distance = ((float)idx * (float)SPEED_OF_LIGHT) / ( (float)(frequencies[1] - frequencies[0]) * 128.0 * 2.0);
+   return distance * (velocity_factor / 100.0);
+}
+
 static inline void
 mark_map(int x, int y)
 {
@@ -1371,9 +1377,7 @@ cell_draw_marker_info(int m, int n, int w, int h)
       frequency_string(buf, sizeof buf, frequencies[idx]);
       cell_drawstring_5x7(w, h, buf, xpos, ypos, 0xffff);
   } else {
-#define SPEED_OF_LIGHT 299792458
-      float distance = ((float)idx * (float)SPEED_OF_LIGHT) / ( (float)(frequencies[1] - frequencies[0]) * 128.0 * 2.0);
-      chsnprintf(buf, sizeof buf, "%.1f m (%d%%)", distance * (velocity_factor / 100.0), velocity_factor);
+      chsnprintf(buf, sizeof buf, "%.1f m (VF=%d%%)", distance_of_index(idx), velocity_factor);
       cell_drawstring_5x7(w, h, buf, xpos, ypos, 0xffff);
   }