diff --git a/main.c b/main.c
index a69a434..dfba1fb 100644
--- a/main.c
+++ b/main.c
@@ -834,6 +834,9 @@ void
 set_sweep_frequency(int type, int32_t freq)
 {
   int cal_applied = cal_status & CALSTAT_APPLY;
+  // negative value indicate overflow, do nothing
+  if (freq < 0)
+    return;
   switch (type) {
   case ST_START:
     freq_mode_startstop();
diff --git a/ui.c b/ui.c
index aa38228..8c9bb71 100644
--- a/ui.c
+++ b/ui.c
@@ -71,9 +71,14 @@ enum {
   KM_START, KM_STOP, KM_CENTER, KM_SPAN, KM_CW, KM_SCALE, KM_REFPOS, KM_EDELAY, KM_VELOCITY_FACTOR, KM_SCALEDELAY
 };
 
+enum {
+  LM_MARKER, LM_SEARCH, LM_CENTER, LM_SPAN
+};
+
 uint8_t ui_mode = UI_NORMAL;
 uint8_t keypad_mode;
 int8_t selection = 0;
+uint8_t lever_mode = LM_MARKER;
 
 typedef struct {
   uint8_t type;
@@ -774,6 +779,7 @@ menu_stimulus_cb(int item)
       ui_mode_keypad(item);
       ui_process_keypad();
     }
+    lever_mode = item == 3 ? LM_SPAN : LM_CENTER;
     break;
   case 5: /* PAUSE */
     toggle_sweep();
@@ -867,6 +873,7 @@ menu_marker_search_cb(int item)
     break;
   }
   redraw_marker(active_marker, TRUE);
+  lever_mode = LM_SEARCH;
 }
 
 void 
@@ -911,6 +918,7 @@ menu_marker_sel_cb(int item)
   }
   redraw_marker(active_marker, TRUE);
   draw_menu();
+  lever_mode = LM_MARKER;
 }
 
 const menuitem_t menu_calop[] = {
@@ -1665,6 +1673,93 @@ ui_mode_normal(void)
   ui_mode = UI_NORMAL;
 }
 
+static void
+lever_move_marker(int status)
+{
+  do {
+    if (active_marker >= 0 && markers[active_marker].enabled) {
+      if ((status & EVT_DOWN) && markers[active_marker].index > 0) {
+        markers[active_marker].index--;
+        markers[active_marker].frequency = frequencies[markers[active_marker].index];
+        redraw_marker(active_marker, FALSE);
+      }
+      if ((status & EVT_UP) && markers[active_marker].index < 100) {
+        markers[active_marker].index++;
+        markers[active_marker].frequency = frequencies[markers[active_marker].index];
+        redraw_marker(active_marker, FALSE);
+      }
+    }
+    status = btn_wait_release();
+  } while (status != 0);
+  if (active_marker >= 0)
+    redraw_marker(active_marker, TRUE);
+}
+
+static void
+lever_search_marker(int status)
+{
+  if (active_marker >= 0) {
+    if (status & EVT_DOWN) {
+      int i = marker_search_left(markers[active_marker].index);
+      if (i != -1)
+        markers[active_marker].index = i;
+    } else if (status & EVT_UP) {
+      int i = marker_search_right(markers[active_marker].index);
+      if (i != -1)
+        markers[active_marker].index = i;
+    }
+    redraw_marker(active_marker, TRUE);
+  }
+}
+
+// ex. 10942 -> 10000
+//      6791 ->  5000
+//       341 ->   200
+static uint32_t
+step_round(uint32_t v)
+{
+  // decade step
+  uint32_t x = 1;
+  for (x = 1; x * 10 < v; x *= 10)
+    ;
+  
+  // 1-2-5 step
+  if (x * 2 > v)
+    return x;
+  else if (x * 5 > v)
+    return x * 2;
+  else 
+    return x * 5;
+}
+
+static void
+lever_zoom_span(int status)
+{
+  if (status & EVT_UP) {
+    uint32_t span = get_sweep_frequency(ST_SPAN);
+    span = step_round(span - 1);
+    set_sweep_frequency(ST_SPAN, span);
+  } else if (status & EVT_DOWN) {
+    uint32_t span = get_sweep_frequency(ST_SPAN);
+    span = step_round(span);
+    span = step_round(span * 3);
+    set_sweep_frequency(ST_SPAN, span);
+  }
+}
+
+static void
+lever_move_center(int status)
+{
+  uint32_t center = get_sweep_frequency(ST_CENTER);
+  uint32_t span = get_sweep_frequency(ST_SPAN);
+  span = step_round(span / 3);
+  if (status & EVT_UP) {
+    set_sweep_frequency(ST_CENTER, center + span);
+  } else if (status & EVT_DOWN) {
+    set_sweep_frequency(ST_CENTER, center - span);
+  }
+}
+
 static void
 ui_process_normal(void)
 {
@@ -1673,23 +1768,12 @@ ui_process_normal(void)
     if (status & EVT_BUTTON_SINGLE_CLICK) {
       ui_mode_menu();
     } else {
-      do {
-        if (active_marker >= 0 && markers[active_marker].enabled) {
-          if ((status & EVT_DOWN) && markers[active_marker].index > 0) {
-            markers[active_marker].index--;
-            markers[active_marker].frequency = frequencies[markers[active_marker].index];
-            redraw_marker(active_marker, FALSE);
-          }
-          if ((status & EVT_UP) && markers[active_marker].index < 100) {
-            markers[active_marker].index++;
-            markers[active_marker].frequency = frequencies[markers[active_marker].index];
-            redraw_marker(active_marker, FALSE);
-          }
-        }
-        status = btn_wait_release();
-      } while (status != 0);
-      if (active_marker >= 0)
-        redraw_marker(active_marker, TRUE);
+      switch (lever_mode) {
+      case LM_MARKER: lever_move_marker(status);   break;
+      case LM_SEARCH: lever_search_marker(status); break;
+      case LM_CENTER: lever_move_center(status);   break;
+      case LM_SPAN:   lever_zoom_span(status);     break;      
+      }
     }
   }
 }