diff --git a/toonz/sources/include/toonz/preferencesitemids.h b/toonz/sources/include/toonz/preferencesitemids.h
index 204c6e5..0e0dbd5 100644
--- a/toonz/sources/include/toonz/preferencesitemids.h
+++ b/toonz/sources/include/toonz/preferencesitemids.h
@@ -130,6 +130,7 @@ enum PreferencesItemId {
   expandFunctionHeader,
   showColumnNumbers,
   parentColorsInXsheetColumn,
+  highlightLineEverySecond,
   syncLevelRenumberWithXsheet,
   currentTimelineEnabled,
   currentColumnColor,
diff --git a/toonz/sources/include/toonz/sceneproperties.h b/toonz/sources/include/toonz/sceneproperties.h
index 145dc1f..c1a258d 100644
--- a/toonz/sources/include/toonz/sceneproperties.h
+++ b/toonz/sources/include/toonz/sceneproperties.h
@@ -197,10 +197,8 @@ Set the distance between two markers to \p distance and \b offset to markers
 offset,
 \sa setMarkers()
   */
-  void getMarkers(int &distance, int &offset) const {
-    distance = m_markerDistance;
-    offset   = m_markerOffset;
-  }
+  void getMarkers(int &distance, int &offset, int &secDistance) const;
+
   /*!
           Sets information about xsheet markers, xsheet horizontal line.
           Sets the distance between two markers to \p distance and \b offset,row
@@ -209,6 +207,7 @@ of first
 \sa getMarkers()
   */
   void setMarkers(int distance, int offset);
+
   /*!
           Returns full-color images subsampling in scene. Subsampling value is
 the simplifying
diff --git a/toonz/sources/include/toonzqt/spreadsheetviewer.h b/toonz/sources/include/toonzqt/spreadsheetviewer.h
index 138a5ff..c067ab8 100644
--- a/toonz/sources/include/toonzqt/spreadsheetviewer.h
+++ b/toonz/sources/include/toonzqt/spreadsheetviewer.h
@@ -312,7 +312,7 @@ class DVAPI SpreadsheetViewer : public QDialog {
   QPoint m_lastAutoPanPos;
   int m_rowCount, m_columnCount;
   int m_currentRow;
-  int m_markRowDistance, m_markRowOffset;
+  int m_markRowDistance, m_markRowOffset, m_markSecRowDistance;
   // QRect m_selectedCells; // x=col, y=row
   bool m_isComputingSize;
   // const Orientation *m_orientation;
@@ -453,17 +453,22 @@ public:
   bool isSelectedCell(int row, int col) const {
     return getSelectedCells().contains(QPoint(col, row));
   }
-  void setMarkRow(int distance, int offset) {
-    m_markRowDistance = distance;  // distance > 0 ? distance : 6;
-    m_markRowOffset   = offset;
+  void setMarkRow(int distance, int offset, int secDistance) {
+    m_markRowDistance    = distance;  // distance > 0 ? distance : 6;
+    m_markRowOffset      = offset;
+    m_markSecRowDistance = secDistance;
   }
   void getMarkRow(int &distance, int &offset) const {
     distance = m_markRowDistance;
     offset   = m_markRowOffset;
   }
-  int isMarkRow(int row) const {
+  bool isMarkRow(int row) const {
     return m_markRowDistance > 0 &&
-           ((row - m_markRowOffset) % m_markRowDistance) == 0;
+           ((row - m_markRowOffset) % m_markRowDistance) == 0 && row > 0;
+  }
+  bool isMarkSecRow(int row) const {
+    return m_markSecRowDistance > 0 &&
+           ((row - m_markRowOffset) % m_markSecRowDistance) == 0 && row > 0;
   }
 
   void setFrameHandle(TFrameHandle *frameHandle);
diff --git a/toonz/sources/toonz/preferencespopup.cpp b/toonz/sources/toonz/preferencespopup.cpp
index 29342c8..4f3b7a6 100644
--- a/toonz/sources/toonz/preferencespopup.cpp
+++ b/toonz/sources/toonz/preferencespopup.cpp
@@ -1257,6 +1257,7 @@ QString PreferencesPopup::getUIString(PreferencesItemId id) {
       {showColumnNumbers, tr("Show Column Numbers in Column Headers")},
       {parentColorsInXsheetColumn,
        tr("Show Column Parent's Color in the Xsheet")},
+      {highlightLineEverySecond, tr("Highlight Line Every Second")},
       {syncLevelRenumberWithXsheet,
        tr("Sync Level Strip Drawing Number Changes with the Xsheet")},
       {currentTimelineEnabled,
@@ -1972,6 +1973,7 @@ QWidget* PreferencesPopup::createXsheetPage() {
   { insertUI(expandFunctionHeader, xshToolbarLay); }
   insertUI(showColumnNumbers, lay);
   insertUI(parentColorsInXsheetColumn, lay);
+  insertUI(highlightLineEverySecond, lay);
   insertUI(syncLevelRenumberWithXsheet, lay);
   insertUI(currentTimelineEnabled, lay);
   insertUI(currentColumnColor, lay);
diff --git a/toonz/sources/toonz/scenesettingspopup.cpp b/toonz/sources/toonz/scenesettingspopup.cpp
index 2856346..52fa68f 100644
--- a/toonz/sources/toonz/scenesettingspopup.cpp
+++ b/toonz/sources/toonz/scenesettingspopup.cpp
@@ -270,8 +270,8 @@ SceneSettingsPopup::SceneSettingsPopup()
   m_tlvSubsamplingFld = new DVGui::IntLineEdit(this, tlvSubsampling, 1);
 
   // Marker Interval - Start Frame
-  int distance, offset;
-  sprop->getMarkers(distance, offset);
+  int distance, offset, secDistance;
+  sprop->getMarkers(distance, offset, secDistance);
   m_markerIntervalFld = new DVGui::IntLineEdit(this, distance, 0);
   m_startFrameFld     = new DVGui::IntLineEdit(this, offset);
 
@@ -294,7 +294,8 @@ SceneSettingsPopup::SceneSettingsPopup()
     // Frame Rate
     mainLayout->addWidget(new QLabel(tr("Frame Rate:"), this), 0, 0,
                           Qt::AlignRight | Qt::AlignVCenter);
-    mainLayout->addWidget(m_frameRateFld, 0, 1);
+    mainLayout->addWidget(m_frameRateFld, 0, 1, 1, 4,
+                          Qt::AlignLeft | Qt::AlignVCenter);
     // Camera BG color
     mainLayout->addWidget(new QLabel(tr("Camera BG Color:"), this), 1, 0,
                           Qt::AlignRight | Qt::AlignVCenter);
@@ -305,7 +306,8 @@ SceneSettingsPopup::SceneSettingsPopup()
     mainLayout->addWidget(m_fieldGuideFld, 2, 1);
     mainLayout->addWidget(new QLabel(tr("A/R:"), this), 2, 2,
                           Qt::AlignRight | Qt::AlignVCenter);
-    mainLayout->addWidget(m_aspectRatioFld, 2, 3);
+    mainLayout->addWidget(m_aspectRatioFld, 2, 3, 1, 2,
+                          Qt::AlignLeft | Qt::AlignVCenter);
     // Image Subsampling  - Tlv Subsampling
     mainLayout->addWidget(new QLabel(tr("Image Subsampling:"), this), 3, 0,
                           Qt::AlignRight | Qt::AlignVCenter);
@@ -362,9 +364,10 @@ SceneSettingsPopup::SceneSettingsPopup()
                          SLOT(onTlvSubsampEditingFinished()));
   // Marker Interval - Start Frame
   ret = ret && connect(m_markerIntervalFld, SIGNAL(editingFinished()), this,
-                       SLOT(onMakerIntervalEditingFinished()));
+                       SLOT(onMakerInformationChanged()));
   ret = ret && connect(m_startFrameFld, SIGNAL(editingFinished()), this,
-                       SLOT(onStartFrameEditingFinished()));
+                       SLOT(onMakerInformationChanged()));
+
   // Use Color Filter and Transparency for Rendering
   ret = ret && connect(m_colorFilterOnRenderCB, SIGNAL(stateChanged(int)), this,
                        SLOT(onColorFilterOnRenderChanged()));
@@ -418,8 +421,8 @@ void SceneSettingsPopup::update() {
   m_fullcolorSubsamplingFld->setValue(sprop->getFullcolorSubsampling());
   if (m_tlvSubsamplingFld)
     m_tlvSubsamplingFld->setValue(sprop->getTlvSubsampling());
-  int markerDistance = 0, markerOffset = 0;
-  sprop->getMarkers(markerDistance, markerOffset);
+  int markerDistance = 0, markerOffset = 0, secDistance;
+  sprop->getMarkers(markerDistance, markerOffset, secDistance);
   m_markerIntervalFld->setValue(markerDistance);
   m_startFrameFld->setValue(markerOffset + 1);
   m_colorFilterOnRenderCB->setChecked(
@@ -494,29 +497,14 @@ void SceneSettingsPopup::onTlvSubsampEditingFinished() {
 
 //-----------------------------------------------------------------------------
 
-void SceneSettingsPopup::onMakerIntervalEditingFinished() {
+void SceneSettingsPopup::onMakerInformationChanged() {
   TSceneProperties *sprop = getProperties();
-  int distance, offset;
-  sprop->getMarkers(distance, offset);
+  int distance, offset, secDistance;
+  sprop->getMarkers(distance, offset, secDistance);
   int markerDistance = m_markerIntervalFld->text().toInt();
   int markerOffset   = m_startFrameFld->text().toInt() - 1;
-  assert(offset == markerOffset);
-  if (distance == markerDistance) return;
-  sprop->setMarkers(markerDistance, markerOffset);
-  TApp::instance()->getCurrentScene()->notifySceneChanged();
-  TApp::instance()->getCurrentXsheet()->notifyXsheetChanged();
-}
-
-//-----------------------------------------------------------------------------
 
-void SceneSettingsPopup::onStartFrameEditingFinished() {
-  TSceneProperties *sprop = getProperties();
-  int distance, offset;
-  sprop->getMarkers(distance, offset);
-  int markerDistance = m_markerIntervalFld->text().toInt();
-  int markerOffset   = m_startFrameFld->text().toInt() - 1;
-  assert(markerDistance == distance);
-  if (offset == markerOffset) return;
+  if (distance == markerDistance && offset == markerOffset) return;
   sprop->setMarkers(markerDistance, markerOffset);
   TApp::instance()->getCurrentScene()->notifySceneChanged();
   TApp::instance()->getCurrentXsheet()->notifyXsheetChanged();
diff --git a/toonz/sources/toonz/scenesettingspopup.h b/toonz/sources/toonz/scenesettingspopup.h
index b6096a8..6108497 100644
--- a/toonz/sources/toonz/scenesettingspopup.h
+++ b/toonz/sources/toonz/scenesettingspopup.h
@@ -76,8 +76,7 @@ public slots:
 
   void onFullColorSubsampEditingFinished();
   void onTlvSubsampEditingFinished();
-  void onMakerIntervalEditingFinished();
-  void onStartFrameEditingFinished();
+  void onMakerInformationChanged();
 
   void setBgColor(const TPixel32 &value, bool isDragging);
 
diff --git a/toonz/sources/toonz/xshcellviewer.cpp b/toonz/sources/toonz/xshcellviewer.cpp
index 8406e2d..a589973 100644
--- a/toonz/sources/toonz/xshcellviewer.cpp
+++ b/toonz/sources/toonz/xshcellviewer.cpp
@@ -1177,32 +1177,42 @@ void CellArea::drawFrameSeparator(QPainter &p, int row, int col,
     layerAxisRange = NumberRange(layerAxis + 1, layerAxis + adjY);
   }
 
-  // mark interval every 6 frames
-  int distance, offset;
+  // mark interval
+  int distance, offset, secDistance;
   TApp::instance()->getCurrentScene()->getScene()->getProperties()->getMarkers(
-      distance, offset);
-  //  if (distance == 0) distance = 6;
+      distance, offset, secDistance);
 
   bool isAfterMarkers =
       distance > 0 && ((row - offset) % distance) == 0 && row != 0;
-  QColor color = isAfterMarkers ? m_viewer->getMarkerLineColor()
-                                : m_viewer->getLightLineColor();
-  color.setAlpha(isAfterMarkers ? m_viewer->getMarkerLineColor().alpha()
-                                : m_viewer->getLightLineColor().alpha());
+  bool isAfterSecMarkers =
+      secDistance > 0 && ((row - offset) % secDistance) == 0 && row != 0;
+
+  QColor color = (isAfterMarkers || isAfterSecMarkers)
+                     ? m_viewer->getMarkerLineColor()
+                     : m_viewer->getLightLineColor();
+  double lineWidth = (isAfterSecMarkers) ? 3. : 1.;
+
+  int frameAxis = m_viewer->rowToFrameAxis(row);
+  int handleSize =
+      (emptyFrame)
+          ? 0
+          : (o->isVerticalTimeline())
+                ? (isAfterMarkers || isAfterSecMarkers)
+                      ? 0
+                      : o->rect(PredefinedRect::DRAG_HANDLE_CORNER).width()
+                : o->rect(PredefinedRect::DRAG_HANDLE_CORNER).height();
 
-  int frameAxis        = m_viewer->rowToFrameAxis(row);
   QLine horizontalLine = m_viewer->orientation()->horizontalLine(
-      frameAxis,
-      layerAxisRange.adjusted((o->isVerticalTimeline() ? 0 : -1), 0));
+      frameAxis, layerAxisRange.adjusted(handleSize - 1, 1));
   if (heldFrame) {
     int x = horizontalLine.x1();
-    int y = horizontalLine.y2() - 1;
+    int y = horizontalLine.y2() - 2;
     horizontalLine.setP1(QPoint(x, y));
     color.setAlpha(120);
   } else if (!o->isVerticalTimeline() && !isAfterMarkers && emptyFrame)
-    color.setAlpha(isAfterMarkers ? m_viewer->getMarkerLineColor().alpha()
-                                  : m_viewer->getLightLineColor().alpha());
-  p.setPen(color);
+    color.setAlpha(m_viewer->getLightLineColor().alpha());
+
+  p.setPen(QPen(color, lineWidth, Qt::SolidLine, Qt::FlatCap));
   p.drawLine(horizontalLine);
 }
 
@@ -1456,10 +1466,9 @@ void CellArea::drawExtenderHandles(QPainter &p) {
           ? QPoint(0, 0)
           : o->point(PredefinedPoint::KEY_HIDDEN);
 
-  int distance, offset;
+  int distance, offset, secDistance;
   TApp::instance()->getCurrentScene()->getScene()->getProperties()->getMarkers(
-      distance, offset);
-  //  if (distance == 0) distance = 6;
+      distance, offset, secDistance);
 
   QPoint xyRadius = o->point(PredefinedPoint::EXTENDER_XY_RADIUS);
 
@@ -1556,12 +1565,12 @@ void CellArea::drawSoundCell(QPainter &p, int row, int col, bool isReference) {
     return;
   }
 
-  if (o->isVerticalTimeline() || !row) drawFrameSeparator(p, row, col, false);
-
   TXshSoundLevelP soundLevel = cell.getSoundLevel();
 
   int r0, r1;
   if (!soundColumn->getLevelRange(row, r0, r1)) {
+    if (o->isVerticalTimeline() || !row) drawFrameSeparator(p, row, col, false);
+
     // only draw mark
     if (markId >= 0) {
       p.setBrush(markColor);
@@ -1608,6 +1617,8 @@ void CellArea::drawSoundCell(QPainter &p, int row, int col, bool isReference) {
   drawEndOfDragHandle(p, isLastRow, xy, cellColor);
   drawLockedDottedLine(p, soundColumn->isLocked(), xy, cellColor);
 
+  if (o->isVerticalTimeline() || !row) drawFrameSeparator(p, row, col, false);
+
   QRect trackRect = o->rect(PredefinedRect::SOUND_TRACK)
                         .adjusted(0, 0, -frameAdj.x(), -frameAdj.y())
                         .translated(xy);
@@ -1693,19 +1704,6 @@ void CellArea::drawSoundCell(QPainter &p, int row, int col, bool isReference) {
     m_soundLevelModifyRects.append(modifierRect);
   }
 
-  int distance, markerOffset;
-  TApp::instance()->getCurrentScene()->getScene()->getProperties()->getMarkers(
-      distance, markerOffset);
-  //  if (distance == 0) distance = 6;
-  bool isAfterMarkers =
-      distance > 0 && ((row - markerOffset) % distance) == 0 && row != 0;
-
-  // draw marker interval
-  if (o->isVerticalTimeline() && isAfterMarkers) {
-    p.setPen(m_viewer->getMarkerLineColor());
-    p.drawLine(o->line(PredefinedLine::SEE_MARKER_THROUGH).translated(xy));
-  }
-
   // cell mark
   if (markId >= 0) {
     p.setBrush(markColor);
@@ -1920,11 +1918,11 @@ void CellArea::drawLevelCell(QPainter &p, int row, int col, bool isReference,
 
   bool heldFrame = (!o->isVerticalTimeline() && sameLevel &&
                     prevCell.m_frameId == cell.m_frameId);
-  drawFrameSeparator(p, row, col, false, heldFrame);
 
   if (cell.isEmpty()) {  // it means previous is not empty
     // diagonal cross meaning end of level
 
+    drawFrameSeparator(p, row, col, true, heldFrame);
     // cell mark
     if (markId >= 0) {
       p.setBrush(markColor);
@@ -2001,18 +1999,7 @@ void CellArea::drawLevelCell(QPainter &p, int row, int col, bool isReference,
 
   drawLockedDottedLine(p, xsh->getColumn(col)->isLocked(), xy, cellColor);
 
-  int distance, offset;
-  TApp::instance()->getCurrentScene()->getScene()->getProperties()->getMarkers(
-      distance, offset);
-  //  if (distance == 0) distance = 6;
-  bool isAfterMarkers =
-      distance > 0 && ((row - offset) % distance) == 0 && row != 0;
-
-  // draw marker interval
-  if (o->isVerticalTimeline() && isAfterMarkers) {
-    p.setPen(m_viewer->getMarkerLineColor());
-    p.drawLine(o->line(PredefinedLine::SEE_MARKER_THROUGH).translated(xy));
-  }
+  drawFrameSeparator(p, row, col, false, heldFrame);
 
   QRect nameRect = o->rect(PredefinedRect::CELL_NAME).translated(QPoint(x, y));
 
@@ -2124,6 +2111,12 @@ void CellArea::drawLevelCell(QPainter &p, int row, int col, bool isReference,
     p.setPen(penColor);
   }
 
+  int distance, offset, secDistance;
+  TApp::instance()->getCurrentScene()->getScene()->getProperties()->getMarkers(
+      distance, offset, secDistance);
+  bool isAfterMarkers =
+      distance > 0 && ((row - offset) % distance) == 0 && row != 0;
+
   // draw level name
   if (showLevelName &&
       (!sameLevel ||
@@ -2220,9 +2213,11 @@ void CellArea::drawSoundTextCell(QPainter &p, int row, int col) {
 
   bool heldFrame = (!o->isVerticalTimeline() && sameLevel &&
                     prevCell.m_frameId == cell.m_frameId);
-  drawFrameSeparator(p, row, col, false, heldFrame);
 
   if (cell.isEmpty()) {  // diagonal cross meaning end of level
+
+    drawFrameSeparator(p, row, col, false, heldFrame);
+
     QColor levelEndColor = m_viewer->getTextColor();
     levelEndColor.setAlphaF(0.3);
     p.setPen(levelEndColor);
@@ -2272,6 +2267,8 @@ void CellArea::drawSoundTextCell(QPainter &p, int row, int col) {
 
   drawLockedDottedLine(p, xsh->getColumn(col)->isLocked(), xy, cellColor);
 
+  drawFrameSeparator(p, row, col, false, heldFrame);
+
   // cell mark
   if (markId >= 0) {
     p.setBrush(markColor);
@@ -2282,19 +2279,6 @@ void CellArea::drawSoundTextCell(QPainter &p, int row, int col) {
   TFrameId fid = cell.m_frameId;
   if (fid.getNumber() - 1 < 0) return;
 
-  int distance, offset;
-  TApp::instance()->getCurrentScene()->getScene()->getProperties()->getMarkers(
-      distance, offset);
-  //  if (distance == 0) distance = 6;
-  bool isAfterMarkers =
-      distance > 0 && ((row - offset) % distance) == 0 && row != 0;
-
-  // draw marker interval
-  if (o->isVerticalTimeline() && isAfterMarkers) {
-    p.setPen(m_viewer->getMarkerLineColor());
-    p.drawLine(o->line(PredefinedLine::SEE_MARKER_THROUGH).translated(xy));
-  }
-
   p.setPen(Qt::black);
   QRect nameRect = o->rect(PredefinedRect::CELL_NAME).translated(QPoint(x, y));
   nameRect.adjust(0, 0, -frameAdj.x(), -frameAdj.y());
@@ -2480,9 +2464,6 @@ void CellArea::drawSoundTextColumn(QPainter &p, int r0, int r1, int col) {
 
     // paint background and other stuffs
     for (auto info : infoList) {
-      bool heldFrame = (!o->isVerticalTimeline() && info.row != row);
-      drawFrameSeparator(p, info.row, col, false, heldFrame);
-
       bool isSelected =
           isColSelected || cellSelection->isCellSelected(info.row, col);
       QColor tmpCellColor = (isSelected) ? selectedCellColor : cellColor;
@@ -2499,6 +2480,9 @@ void CellArea::drawSoundTextColumn(QPainter &p, int r0, int r1, int col) {
       drawEndOfDragHandle(p, info.row == rowTo, info.xy, tmpCellColor);
       drawLockedDottedLine(p, xsh->getColumn(col)->isLocked(), info.xy,
                            tmpCellColor);
+
+      bool heldFrame = (!o->isVerticalTimeline() && info.row != row);
+      drawFrameSeparator(p, info.row, col, false, heldFrame);
       // draw mark
       if (info.markId >= 0) {
         p.setBrush(info.markColor);
@@ -2625,13 +2609,6 @@ void CellArea::drawPaletteCell(QPainter &p, int row, int col,
 
   bool sameLevel = prevCell.m_level.getPointer() == cell.m_level.getPointer();
 
-  int distance, offset;
-  TApp::instance()->getCurrentScene()->getScene()->getProperties()->getMarkers(
-      distance, offset);
-  //  if (distance == 0) distance = 6;
-  bool isAfterMarkers =
-      distance > 0 && ((row - offset) % distance) == 0 && row != 0;
-
   bool isRed           = false;
   TXshPaletteLevel *pl = cell.getPaletteLevel();
   if (pl && !pl->getPalette()) isRed = true;
@@ -2695,11 +2672,20 @@ void CellArea::drawPaletteCell(QPainter &p, int row, int col,
     return;
   }
 
+  int distance, offset, secDistance;
+  TApp::instance()->getCurrentScene()->getScene()->getProperties()->getMarkers(
+      distance, offset, secDistance);
+
+  bool isAfterMarkers =
+      distance > 0 && ((row - offset) % distance) == 0 && row != 0;
+
   bool heldFrame = (!o->isVerticalTimeline() && !isAfterMarkers && sameLevel &&
                     prevCell.m_frameId == cell.m_frameId);
-  drawFrameSeparator(p, row, col, false, heldFrame);
 
   if (cell.isEmpty()) {  // this means the former is not empty
+
+    drawFrameSeparator(p, row, col, false, heldFrame);
+
     QColor levelEndColor = m_viewer->getTextColor();
     levelEndColor.setAlphaF(0.3);
     p.setPen(levelEndColor);
@@ -2753,10 +2739,7 @@ void CellArea::drawPaletteCell(QPainter &p, int row, int col,
   drawEndOfDragHandle(p, isLastRow, xy, cellColor);
   drawLockedDottedLine(p, xsh->getColumn(col)->isLocked(), xy, cellColor);
 
-  if (o->isVerticalTimeline() && isAfterMarkers) {
-    p.setPen(m_viewer->getMarkerLineColor());
-    p.drawLine(o->line(PredefinedLine::SEE_MARKER_THROUGH).translated(xy));
-  }
+  drawFrameSeparator(p, row, col, false, heldFrame);
 
   if (sameLevel && prevCell.m_frameId == cell.m_frameId &&
       !isAfterMarkers) {  // cell equal to previous one (not on marker line):
diff --git a/toonz/sources/toonz/xsheetviewer.cpp b/toonz/sources/toonz/xsheetviewer.cpp
index 797b676..aa4a0a8 100644
--- a/toonz/sources/toonz/xsheetviewer.cpp
+++ b/toonz/sources/toonz/xsheetviewer.cpp
@@ -1163,12 +1163,12 @@ void XsheetViewer::wheelEvent(QWheelEvent *event) {
       return;
     }
 
-    int markerDistance = 0, markerOffset = 0;
+    int markerDistance = 0, markerOffset = 0, secDistance;
     TApp::instance()
         ->getCurrentScene()
         ->getScene()
         ->getProperties()
-        ->getMarkers(markerDistance, markerOffset);
+        ->getMarkers(markerDistance, markerOffset, secDistance);
 
     if (event->angleDelta().x() == 0) {  // vertical scroll
       if (!orientation()->isVerticalTimeline()) markerDistance = 1;
diff --git a/toonz/sources/toonz/xshrowviewer.cpp b/toonz/sources/toonz/xshrowviewer.cpp
index c20bf6d..4af1bd8 100644
--- a/toonz/sources/toonz/xshrowviewer.cpp
+++ b/toonz/sources/toonz/xshrowviewer.cpp
@@ -106,9 +106,9 @@ void RowArea::drawRows(QPainter &p, int r0, int r1) {
   p.setFont(font);
 
   // marker interval
-  int distance, offset;
+  int distance, offset, secDistance;
   TApp::instance()->getCurrentScene()->getScene()->getProperties()->getMarkers(
-      distance, offset);
+      distance, offset, secDistance);
 
   // default value
   //  if (distance == 0) distance = 6;
@@ -131,9 +131,16 @@ void RowArea::drawRows(QPainter &p, int r0, int r1) {
     //--- draw horizontal line
     bool isAfterMarkers =
         (distance > 0 && ((r - offset) % distance) == 0 && r != 0);
-    QColor color = isAfterMarkers ? m_viewer->getMarkerLineColor()
-                                  : m_viewer->getLightLineColor();
-    p.setPen(color);
+    bool isAfterSecMarkers =
+        secDistance > 0 && ((r - offset) % secDistance) == 0 && r != 0;
+
+    QColor color = (isAfterSecMarkers || isAfterMarkers)
+                       ? m_viewer->getMarkerLineColor()
+                       : m_viewer->getLightLineColor();
+
+    p.setPen(
+        QPen(color, (isAfterSecMarkers) ? 3. : 1., Qt::SolidLine, Qt::FlatCap));
+    // p.setPen(color);
     QLine horizontalLine = o->horizontalLine(frameAxis, layerSide);
     if (!o->isVerticalTimeline()) {
       int x = horizontalLine.x1();
diff --git a/toonz/sources/toonzlib/preferences.cpp b/toonz/sources/toonzlib/preferences.cpp
index 5bec8d7..e4dae07 100644
--- a/toonz/sources/toonzlib/preferences.cpp
+++ b/toonz/sources/toonzlib/preferences.cpp
@@ -580,6 +580,8 @@ void Preferences::definePreferenceItems() {
   define(showColumnNumbers, "showColumnNumbers", QMetaType::Bool, false);
   define(parentColorsInXsheetColumn, "parentColorsInXsheetColumn",
          QMetaType::Bool, false);
+  define(highlightLineEverySecond, "highlightLineEverySecond", QMetaType::Bool,
+         false);
   define(syncLevelRenumberWithXsheet, "syncLevelRenumberWithXsheet",
          QMetaType::Bool, true);
   define(currentTimelineEnabled, "currentTimelineEnabled", QMetaType::Bool,
diff --git a/toonz/sources/toonzlib/sceneproperties.cpp b/toonz/sources/toonzlib/sceneproperties.cpp
index fc0bb34..f167771 100644
--- a/toonz/sources/toonzlib/sceneproperties.cpp
+++ b/toonz/sources/toonzlib/sceneproperties.cpp
@@ -140,6 +140,19 @@ void TSceneProperties::setBgColor(const TPixel32 &color) { m_bgColor = color; }
 
 //-----------------------------------------------------------------------------
 
+void TSceneProperties::getMarkers(int &distance, int &offset,
+                                  int &secDistance) const {
+  distance = m_markerDistance;
+  offset   = m_markerOffset;
+  // TODO: handle drop frame when the fps has decimal part
+  secDistance =
+      (Preferences::instance()->getBoolValue(highlightLineEverySecond))
+          ? (int)std::round(getOutputProperties()->getFrameRate())
+          : -1;
+}
+
+//-----------------------------------------------------------------------------
+
 void TSceneProperties::setMarkers(int distance, int offset) {
   m_markerDistance = distance;
   m_markerOffset   = offset;
diff --git a/toonz/sources/toonzqt/functionviewer.cpp b/toonz/sources/toonzqt/functionviewer.cpp
index c4f7a25..a62fbb3 100644
--- a/toonz/sources/toonzqt/functionviewer.cpp
+++ b/toonz/sources/toonzqt/functionviewer.cpp
@@ -371,9 +371,9 @@ void FunctionViewer::refreshModel() {
 
     m_treeView->setCurrentScenePath(scenePath);
 
-    int distance, offset;
-    scene->getProperties()->getMarkers(distance, offset);
-    m_numericalColumns->setMarkRow(distance, offset);
+    int distance, offset, secDistance;
+    scene->getProperties()->getMarkers(distance, offset, secDistance);
+    m_numericalColumns->setMarkRow(distance, offset, secDistance);
   }
 
   m_treeView->updateAll();
diff --git a/toonz/sources/toonzqt/spreadsheetviewer.cpp b/toonz/sources/toonzqt/spreadsheetviewer.cpp
index 4ebced3..dff1065 100644
--- a/toonz/sources/toonzqt/spreadsheetviewer.cpp
+++ b/toonz/sources/toonzqt/spreadsheetviewer.cpp
@@ -376,10 +376,11 @@ void RowPanel::drawRows(QPainter &p, int r0, int r1) {
   for (r = r0; r <= r1; r++) {
     int next_y = getViewer()->rowToY(r + 1);
     // draw horizontal line
-    QColor color = (getViewer()->isMarkRow(r))
+    bool isMarkSecRow = getViewer()->isMarkSecRow(r);
+    QColor color      = (isMarkSecRow || getViewer()->isMarkRow(r))
                        ? getViewer()->getMarkerLineColor()
                        : getViewer()->getLightLineColor();
-    p.setPen(color);
+    p.setPen(QPen(color, (isMarkSecRow) ? 3. : 1., Qt::SolidLine, Qt::FlatCap));
     p.drawLine(x0, y, x1, y);
 
     if (simpleView && r > 0 && !getViewer()->isMarkRow(r + 1)) {
@@ -395,11 +396,6 @@ void RowPanel::drawRows(QPainter &p, int r0, int r1) {
                Qt::AlignVCenter | Qt::AlignRight, number);
     y = next_y;
   }
-  // erase the marker interval at upper-end
-  if (r0 == 0) {
-    p.setPen(getViewer()->getLightLineColor());
-    p.drawLine(x0, getViewer()->rowToY(0), x1, getViewer()->rowToY(0));
-  }
 }
 
 //-----------------------------------------------------------------------------
@@ -493,15 +489,15 @@ void CellPanel::paintEvent(QPaintEvent *e) {
   // draw rows
   int currentRow = getViewer()->getCurrentRow();
   for (int r = r0; r <= r1; r++) {
-    int y        = getViewer()->rowToY(r);
-    QColor color = getViewer()->isMarkRow(r) ? getViewer()->getMarkerLineColor()
-                                             : getViewer()->getLightLineColor();
-    painter.setPen(color);
+    int y             = getViewer()->rowToY(r);
+    bool isMarkSecRow = getViewer()->isMarkSecRow(r);
+    QColor color      = (isMarkSecRow || getViewer()->isMarkRow(r))
+                       ? getViewer()->getMarkerLineColor()
+                       : getViewer()->getLightLineColor();
+    painter.setPen(
+        QPen(color, (isMarkSecRow) ? 3. : 1., Qt::SolidLine, Qt::FlatCap));
     painter.drawLine(x0, y, x1, y);
   }
-  // erase the marker interval at upper-end
-  painter.setPen(getViewer()->getLightLineColor());
-  painter.drawLine(x0, 0, x1, 0);
 }
 
 }  // namespace Spreadsheet
@@ -525,6 +521,7 @@ SpreadsheetViewer::SpreadsheetViewer(QWidget *parent)
     , m_currentRow(0)
     , m_markRowDistance(6)
     , m_markRowOffset(0)
+    , m_markSecRowDistance(-1)
     , m_isComputingSize(false)
     , m_frameScroller() {
   // m_orientation = Orientations::topToBottom ();