diff --git a/frontend/src/Main.elm b/frontend/src/Main.elm
index 0355696..9b9e012 100644
--- a/frontend/src/Main.elm
+++ b/frontend/src/Main.elm
@@ -63,11 +63,7 @@ init _ url navKey =
             case Url.Parser.parse routeParser url of
                 Just (Timeline (Just s) (Just d)) -> (toFloat s, toFloat d)
                 _ -> (10,10)
-    in
-        ((Model
-              (toCoord (Pos 0 0 Nothing))
-              (ZoomLevel 0) Nothing 0 0 (0,0) Loading),
-             (fetchTrack start duration))
+    in (Model.empty, fetchTrack start duration)
 
 -- SUBSCRIPTIONS
 
@@ -116,18 +112,17 @@ dragUpdate model (newx, newy) =
           let t = subtractTuple fromxy (newx, newy)
           in { model | centre = translate fromcoord (pixelsToCoord model.zoom t) }
       Just (DragGraph (fromx,_) fromtime) ->
-          let time = secondsFromPixels model (fromx - newx)
-          in { model | startTime = fromtime + time }
-      Just (DragLeftMark (fromx,_) (fromtime, fromduration)) ->
           let time = secondsFromPixels model (fromx - newx)
           in { model |
-                   markedTime = ((fromtime - time),
-                                     (max (fromduration + time) 0))
+                   startTime = fromtime + time
              }
-      Just (DragRightMark (fromx,_) fromduration) ->
+      Just (DragLeftMark (fromx,_) fromtime) ->
           let time = secondsFromPixels model (fromx - newx)
-          in { model | markedTime = (Tuple.first model.markedTime,
-                                         (max (fromduration - time) 0)) }
+          in { model | leftMark = fromtime - time
+                   , rightMark = max (fromtime - time) model.rightMark }
+      Just (DragRightMark (fromx,_) fromtime) ->
+          let time = secondsFromPixels model (fromx - newx)
+          in { model | rightMark = max (fromtime - time) model.leftMark }
 
 
 
@@ -149,13 +144,12 @@ updateModel msg model =
         TimeScale factor ->
             let startTime = model.startTime + factor / 2
                 duration = model.duration - factor
+                clampVisible = clamp startTime (startTime + duration)
             in { model |
                   startTime = startTime
             ,     duration = duration
-            ,     markedTime =
-                  let (s, d) = model.markedTime
-                  in ( max s startTime
-                     , (min (s + d) (startTime + duration)) - s)
+            ,     leftMark = clampVisible model.leftMark
+            ,     rightMark = clampVisible model.rightMark
             }
 
         Loaded result ->
@@ -170,7 +164,8 @@ updateModel msg model =
                         , zoom = ZoomLevel (13  * 8)
                         , startTime = start
                         , duration = duration
-                        , markedTime = (start + 300, duration - 900)
+                        , leftMark = start
+                        , rightMark = start + duration
                     }
                 Err (Http.BadBody e) -> { model | track = Debug.log e (Failure "e") }
                 Err e -> { model | track = Debug.log "unknown error" (Failure "e") }
@@ -346,9 +341,9 @@ handleDragMark model e =
     let epos ev = Tuple.mapBoth floor floor ev.pointer.clientPos
     in case e.targetId of
         "left-marker" ->
-            DragStart (DragLeftMark (epos e.pointerEvent) model.markedTime)
+            DragStart (DragLeftMark (epos e.pointerEvent) model.leftMark)
         "right-marker" ->
-            DragStart (DragRightMark (epos e.pointerEvent) (Tuple.second model.markedTime))
+            DragStart (DragRightMark (epos e.pointerEvent) model.rightMark)
         _ -> Dribble "drag with unknown target"
 
 
@@ -409,13 +404,9 @@ timeAxis model points =
                 , strokeWidth "3"
                 ] []
         markStartPix =
-            case model.markedTime of
-                (s, d) ->
-                    floor ((s  - startTime) * portalWidth/maxX)
+            floor ((model.leftMark - startTime) * portalWidth/maxX)
         markEndPix =
-            case model.markedTime of
-                (s, d) ->
-                    ceiling ((s - startTime + d) * portalWidth/maxX)
+            ceiling ((model.rightMark - startTime) * portalWidth/maxX)
     in
         svg
         [ width portalWidth
diff --git a/frontend/src/Model.elm b/frontend/src/Model.elm
index de95cc6..332ae2c 100644
--- a/frontend/src/Model.elm
+++ b/frontend/src/Model.elm
@@ -3,14 +3,16 @@ module Model exposing
       Model
     , TrackState(..)
     , DragState(..)
+    , empty
     )
-import TileMap exposing (ZoomLevel, Coord)
+import TileMap exposing (ZoomLevel(..), Coord, toCoord)
 import Point exposing (Point)
+import Pos exposing (Pos)
 
 type DragState =
     DragMap (Int, Int) Coord
   | DragGraph (Int, Int) Float
-  | DragLeftMark (Int, Int) (Float, Float)
+  | DragLeftMark (Int, Int) Float
   | DragRightMark (Int, Int) Float
 
 type TrackState = Empty | Loading | Failure String | Present (List Point)
@@ -21,5 +23,14 @@ type alias Model =
     , drag: Maybe DragState
     , startTime : Float
     , duration : Float
-    , markedTime : (Float, Float)
+    , leftMark : Float
+    , rightMark : Float
     , track: TrackState }
+
+empty = Model
+        (toCoord (Pos 0 0 Nothing))
+        (ZoomLevel 0)
+        Nothing
+        0 0
+        0 0
+        Loading