diff --git a/web/app/sketcher/actions/constraintActions.js b/web/app/sketcher/actions/constraintActions.js
index 72f598b9..fc398de5 100644
--- a/web/app/sketcher/actions/constraintActions.js
+++ b/web/app/sketcher/actions/constraintActions.js
@@ -153,6 +153,25 @@ export default [
     }
   },
 
+  {
+    id: 'Horizontal',
+    shortName: 'Horizontal',
+    description: 'Horizontal',
+    selectionMatcher: (selection, sortedByType) => matchAll(sortedByType, Segment, 1),
+
+    invoke: ctx => {
+      const {viewer} = ctx;
+      const pm = viewer.parametricManager;
+
+      viewer.selected.forEach(obj => {
+        const constr = new AlgNumConstraint(ConstraintDefinitions.Horizontal, [obj]);
+        constr.initConstants();
+        pm._add(constr);
+      });
+      pm.commit();
+    }
+  },
+
   {
     id: 'AngleBetween',
     shortName: 'Angle Between',
diff --git a/web/app/sketcher/constr/ANConstraints.js b/web/app/sketcher/constr/ANConstraints.js
index b59f5342..ad43c95d 100644
--- a/web/app/sketcher/constr/ANConstraints.js
+++ b/web/app/sketcher/constr/ANConstraints.js
@@ -165,10 +165,35 @@ export const ConstraintDefinitions = {
         type: 'number',
         description: 'line angle',
         initialValue: ([seg]) => {
-          const angleFromNormal = seg.getAngleFromNormal();
+          const angleFromNormal = seg.angleDeg();
           return Math.abs(270 - angleFromNormal) > Math.abs(90 - angleFromNormal) ? 90 : 270;
         },
-        transform: degree => ( (degree ) % 360 ) * DEG_RAD
+        transform: degree => degree * DEG_RAD
+      }
+    },
+
+    defineParamsScope: (objs, cb) => {
+      ConstraintDefinitions.Angle.defineParamsScope(objs, cb);
+    },
+
+    collectPolynomials: (polynomials, params, constants) => {
+      ConstraintDefinitions.Angle.collectPolynomials(polynomials, params, constants);
+    }
+  },
+
+  Horizontal: {
+    id: 'Horizontal',
+    name: 'Line Horizontality',
+    constants: {
+      angle: {
+        readOnly: true,
+        type: 'number',
+        description: 'line angle',
+        initialValue: ([seg]) => {
+          const ang = seg.angleDeg();
+          return Math.abs(180 - ang) > Math.min(Math.abs(360 - ang), Math.abs(0 - ang)) ? 0 : 180;
+        },
+        transform: degree => degree * DEG_RAD
       }
     },
 
diff --git a/web/app/sketcher/constr/AlgNumSystem.js b/web/app/sketcher/constr/AlgNumSystem.js
index 23a087bd..c96383ef 100644
--- a/web/app/sketcher/constr/AlgNumSystem.js
+++ b/web/app/sketcher/constr/AlgNumSystem.js
@@ -26,6 +26,8 @@ export class AlgNumSubSystem {
 
   interactiveParams = new Set();
 
+  controlBounds = false;
+
   snapshot = new Map();
 
   constructor() {
@@ -332,7 +334,7 @@ export class AlgNumSubSystem {
         }
       }
       if (isolation.length) {
-        clusters.push(new Isolation(isolation));
+        clusters.push(new Isolation(isolation, this));
       }
     }
 
@@ -428,7 +430,8 @@ export class AlgNumSubSystem {
 
 class Isolation {
 
-  constructor(polynomials) {
+  constructor(polynomials, system) {
+    this.system = system;
     this.polynomials = polynomials;
     this.beingSolvedParams = new Set();
     const residuals = [];
@@ -468,8 +471,10 @@ class Isolation {
     this.beingSolvedParams.forEach(solverParam => {
       let val = solverParam.objectParam.get();
 
-      if (solverParam.objectParam.min && val < solverParam.objectParam.min) {
-        val = solverParam.objectParam.min;
+      if (this.system.controlBounds) {
+        if (solverParam.objectParam.min && val < solverParam.objectParam.min) {
+          val = solverParam.objectParam.min;
+        }
       }
       solverParam.set(val);
     });
diff --git a/web/app/sketcher/shapes/arc.js b/web/app/sketcher/shapes/arc.js
index ee615a7c..dcb59024 100644
--- a/web/app/sketcher/shapes/arc.js
+++ b/web/app/sketcher/shapes/arc.js
@@ -94,7 +94,9 @@ export class Arc extends SketchObject {
     } else {
       endAngle = makeAngle0_360(this.getEndAngle());
     }
-    ctx.arc(this.c.x, this.c.y, r, startAngle, endAngle);
+    if (r > 0) {
+      ctx.arc(this.c.x, this.c.y, r, startAngle, endAngle);
+    }
     let distanceB = this.distanceB();
     if (Math.abs(r - distanceB) * scale > 1) {
       let adj = r / distanceB;
diff --git a/web/app/sketcher/shapes/circle.js b/web/app/sketcher/shapes/circle.js
index 23b56c6c..db20aa46 100644
--- a/web/app/sketcher/shapes/circle.js
+++ b/web/app/sketcher/shapes/circle.js
@@ -32,7 +32,10 @@ export class Circle extends SketchObject {
   
   drawImpl(ctx, scale) {
     ctx.beginPath();
-    ctx.arc(this.c.x, this.c.y, this.r.get(), 0, 2 * Math.PI);
+    let r = this.r.get();
+    if (r > 0) {
+      ctx.arc(this.c.x, this.c.y, r, 0, 2 * Math.PI);
+    }
     ctx.stroke();
   }
   
diff --git a/web/app/sketcher/shapes/segment.js b/web/app/sketcher/shapes/segment.js
index 3c3fdc99..1deb863c 100644
--- a/web/app/sketcher/shapes/segment.js
+++ b/web/app/sketcher/shapes/segment.js
@@ -46,10 +46,15 @@ export class Segment extends SketchObject {
   }
 
   getAngleFromNormal() {
+    return this.angleDeg();
+  }
+
+  angleDeg() {
     const degrees = this.params.ang.get() / DEG_RAD;
     return (degrees + 360) % 360;
   }
 
+
   syncGeometry() {
     const dx = this.b.x - this.a.x;
     const dy = this.b.y - this.a.y;
diff --git a/web/app/sketcher/tools/drag.js b/web/app/sketcher/tools/drag.js
index e9862bc0..fc34f82f 100644
--- a/web/app/sketcher/tools/drag.js
+++ b/web/app/sketcher/tools/drag.js
@@ -37,12 +37,14 @@ export class DragTool extends Tool {
     this.origin.y = e.offsetY;
     this.viewer.screenToModel2(e.offsetX, e.offsetY, this._point);
 
+    this.viewer.parametricManager.algNumSystem.controlBounds = true;
     this.viewer.parametricManager.prepare([this.obj]);
   }
 
   mouseup(e) {
     this.viewer.parametricManager.solve(false);
     this.viewer.refresh();
+    this.viewer.parametricManager.algNumSystem.controlBounds = false;
     this.viewer.toolManager.releaseControl();
     var traveled = math.distance(this.origin.x, this.origin.y, e.offsetX, e.offsetY);
     if (traveled >= 10) {
diff --git a/web/app/sketcher/viewer2d.js b/web/app/sketcher/viewer2d.js
index 32a4f047..d07b10d7 100644
--- a/web/app/sketcher/viewer2d.js
+++ b/web/app/sketcher/viewer2d.js
@@ -239,7 +239,11 @@ class Viewer {
             obj.accept((obj) => {
               if (!obj.visible) return true;
               if (drawPredicate(obj)) {
-                this.__draw(ctx, layer, obj);
+                try {
+                  this.__draw(ctx, layer, obj);
+                } catch (e) {
+                  console.log(e);
+                }
               }
               return true;
             });