diff --git a/src/modules/annotate/dim_continue.rs b/src/modules/annotate/dim_continue.rs
index 7ae3ec92f..bf4f22046 100644
--- a/src/modules/annotate/dim_continue.rs
+++ b/src/modules/annotate/dim_continue.rs
@@ -31,9 +31,12 @@ pub struct DimContinueCommand {
     chain_p1: Vec3,
     /// Direction along the dimension axis (0.0 = horizontal, PI/2 = vertical).
     rotation: f64,
-    /// Perpendicular distance from the extension-line axis to the dimension line.
-    /// Preserved from the base dimension.
-    dim_offset: f32,
+    /// Absolute perpendicular coordinate (dot with `perp`) of the base
+    /// dimension line. Each continued dim line is projected onto this exact
+    /// coordinate so the whole chain stays collinear — even when the extension
+    /// origins sit at different perpendicular positions (extension lines of
+    /// different lengths). (#151)
+    dim_line_perp: f32,
     /// Direction of "up" perpendicular to the dim axis (points toward the dim line).
     perp: Vec3,
     /// True once we have a base dimension loaded.
@@ -46,7 +49,7 @@ impl DimContinueCommand {
         Self {
             chain_p1: Vec3::ZERO,
             rotation: 0.0,
-            dim_offset: 0.0,
+            dim_line_perp: 0.0,
             perp: Vec3::Y,
             ready: false,
         }
@@ -54,20 +57,24 @@ impl DimContinueCommand {
 
     /// Build from the last placed dimension.
     ///
-    /// `p1` / `p2` — extension line origins of the base dim.
-    /// `definition_point` — where the dim line was placed (defines perpendicular offset).
+    /// `p2` — second extension line origin of the base dim (the chain starts
+    ///   here). `p1` is unused — the dim line position comes from
+    ///   `definition_point` alone — but kept for signature parity with the
+    ///   shared `find_last_linear_dim` tuple (DIMBASELINE uses p1).
+    /// `definition_point` — where the dim line was placed; its perpendicular
+    ///   coordinate is the line the whole chain stays collinear with.
     /// `rotation` — 0.0 = horizontal dim, PI/2 = vertical dim.
-    pub fn from_base(p1: Vec3, p2: Vec3, definition_point: Vec3, rotation: f64) -> Self {
+    pub fn from_base(_p1: Vec3, p2: Vec3, definition_point: Vec3, rotation: f64) -> Self {
         // Axis unit vector along the measurement direction — the base dim's
         // rotation angle (any angle, incl. a UCS-aligned one), not a world H/V.
         let axis = Vec3::new(rotation.cos() as f32, rotation.sin() as f32, 0.0);
         // Perpendicular unit vector toward the dim line.
         let perp = Vec3::new(-axis.y, axis.x, 0.0);
-        let dim_offset = (definition_point - p1).dot(perp);
+        let dim_line_perp = definition_point.dot(perp);
         Self {
             chain_p1: p2,
             rotation,
-            dim_offset,
+            dim_line_perp,
             perp,
             ready: true,
         }
@@ -98,11 +105,15 @@ impl CadCommand for DimContinueCommand {
         let mut dim = DimensionLinear::new(v3(p1), v3(p2));
         dim.rotation = self.rotation;
 
-        // Dim-line position: same perpendicular distance as base.
-        let dim_line_pt = p1 + self.perp * self.dim_offset;
-        dim.definition_point = v3(dim_line_pt);
-        dim.base.definition_point = v3(dim_line_pt);
-        dim.base.text_middle_point = v3((dim_line_pt + (p2 + self.perp * self.dim_offset)) * 0.5);
+        // Dim line stays collinear with the base: project both extension
+        // origins onto the base dim line's absolute perpendicular coordinate.
+        // (A fixed offset from p1 drifts off the base line whenever p1 and p2
+        // sit at different perpendicular positions.) (#151)
+        let d1 = p1 + self.perp * (self.dim_line_perp - p1.dot(self.perp));
+        let d2 = p2 + self.perp * (self.dim_line_perp - p2.dot(self.perp));
+        dim.definition_point = v3(d1);
+        dim.base.definition_point = v3(d1);
+        dim.base.text_middle_point = v3((d1 + d2) * 0.5);
         dim.base.insertion_point = dim.base.text_middle_point;
         dim.base.actual_measurement = dim.measurement();
 
@@ -121,8 +132,8 @@ impl CadCommand for DimContinueCommand {
             return None;
         }
         let p1 = self.chain_p1;
-        let dim_line_pt = p1 + self.perp * self.dim_offset;
-        let dim_line_pt2 = pt + self.perp * self.dim_offset;
+        let dim_line_pt = p1 + self.perp * (self.dim_line_perp - p1.dot(self.perp));
+        let dim_line_pt2 = pt + self.perp * (self.dim_line_perp - pt.dot(self.perp));
         Some(WireModel {
             name: "dimcont_preview".into(),
             points: vec![