diff --git a/gui_client.py b/gui_client.py
index 2bbe935..3985340 100644
--- a/gui_client.py
+++ b/gui_client.py
@@ -390,6 +390,16 @@ class TimeAxisItem(pg.AxisItem):
         return [datetime.fromtimestamp(v).strftime("%H:%M:%S") for v in values]
 
 
+class PlotViewBox(pg.ViewBox):
+    """ViewBox with axis-selective wheel zoom: plain wheel → X, Shift+wheel → Y."""
+    def wheelEvent(self, ev, axis=None):
+        if ev.modifiers() & Qt.ShiftModifier:
+            axis = 1   # Y only
+        else:
+            axis = 0   # X only
+        super().wheelEvent(ev, axis=axis)
+
+
 class PlotTooltip(QWidget):
     """Floating value readout that follows the crosshair cursor."""
     def __init__(self, parent: QWidget):
@@ -523,6 +533,7 @@ class PlotTab(QWidget):
             pw = pg.PlotWidget(
                 background="#12121e",
                 axisItems={"bottom": TimeAxisItem(orientation="bottom")},
+                viewBox=PlotViewBox(),
             )
             pw.showGrid(x=True, y=True, alpha=0.3)
             pw.addLegend(offset=(0, 0), labelTextSize="8pt")