diff --git a/web/app/sketcher/parametric.js b/web/app/sketcher/parametric.js
index 646b7570..0b0b15d1 100644
--- a/web/app/sketcher/parametric.js
+++ b/web/app/sketcher/parametric.js
@@ -23,8 +23,8 @@ function ParametricManager(viewer) {
   this.listeners = [];
   this.constantTable = {};
   
-  this.viewer.params.define("constantDefinition", null);
-  this.viewer.params.subscribe("constantDefinition", "parametricManager", this.rebuildConstantTable, this)();
+  this.viewer.params.define('constantDefinition', null);
+  this.viewer.params.subscribe('constantDefinition', 'parametricManager', this.onConstantsExternalChange, this)();
   this.constantResolver = this.createConstantResolver();
 }
 
@@ -61,15 +61,31 @@ ParametricManager.prototype.rebuildConstantTable = function(constantDefinition)
       try {
         var value = eval(prefix + "return " + m[2] + "; \n})()");
         this.constantTable[constant] = value;
-        prefix += constant + " = " + value + ";\n"
+        prefix += "const " + constant + " = " + value + ";\n"
       } catch(e) {
         console.log(e);
       }
     }
   }
+};
+
+ParametricManager.prototype.onConstantsExternalChange = function(constantDefinition) {
+  this.rebuildConstantTable(constantDefinition);
   this.refresh();
 };
 
+ParametricManager.prototype.defineNewConstant = function(name, value) {
+  let constantDefinition = this.viewer.params.constantDefinition;
+  let constantText = name + ' = ' + value;
+  if (constantDefinition) {
+    constantDefinition += '\n' + constantText;
+  } else {
+    constantDefinition = constantText;
+  }
+  this.rebuildConstantTable(constantDefinition);
+  //disabling onConstantsExternalChange since we don't need re-solve  
+  this.viewer.params.set('constantDefinition', constantDefinition, 'parametricManager');
+};
 
 ParametricManager.prototype.findComponents = function(constr) {
   if (this.subSystems.length === 0) {
@@ -500,7 +516,7 @@ ParametricManager.prototype._prepare = function(locked, subSystems, extraConstra
   for (var i = 0; i < subSystems.length; i++) {
     solvers.push(this.prepareForSubSystem(locked, subSystems[i].constraints, extraConstraints, disabledObjects));
   }
-  if (subSystems.length == 0 && locked.length != 0) {
+  if (subSystems.length == 0 && locked && locked.length != 0) {
     solvers.push(this.prepareForSubSystem(locked, [], extraConstraints, disabledObjects));
   }
   return {
@@ -896,9 +912,9 @@ Constraints.RadiusOffset = function(arc1, arc2, offset) {
 Constraints.RadiusOffset.prototype.NAME = 'RadiusOffset';
 Constraints.RadiusOffset.prototype.UI_NAME = 'Radius Offset';
 
-Constraints.RadiusOffset.prototype.getSolveData = function() {
+Constraints.RadiusOffset.prototype.getSolveData = function(resolver) {
   return [
-    ['Diff', [this.arc1.r, this.arc2.r], [this.offset]]
+    ['Diff', [this.arc1.r, this.arc2.r], [resolver(this.offset)]]
   ];
 };
 
diff --git a/web/app/sketcher/tools/offset.js b/web/app/sketcher/tools/offset.js
index db2d9c47..31a11df5 100644
--- a/web/app/sketcher/tools/offset.js
+++ b/web/app/sketcher/tools/offset.js
@@ -28,7 +28,6 @@ export class OffsetTool extends LoopPickTool {
     if (isNaN(delta)) {
       return;
     }
-    const absDelta = Math.abs(delta);
 
     const edges = [];
     const startPoint = findLowestPoint(loopPoints);
@@ -45,7 +44,9 @@ export class OffsetTool extends LoopPickTool {
     if (inverse) {
       delta *= -1;
     }
-    
+
+    const pm = this.viewer.parametricManager;
+    const offsetConstant = createOffsetConstant(pm, delta);
     for (let i = 0; i < length; ++i) {
       let a = loopPoints[pos(i)];
       let b = loopPoints[pos(i + 1)];
@@ -59,8 +60,8 @@ export class OffsetTool extends LoopPickTool {
       if (origEdge._class == 'TCAD.TWO.Segment') {
         const segment = this.viewer.addSegment(aOffX, aOffY, 
                                                bOffX, bOffY, this.viewer.activeLayer);
-        this.viewer.parametricManager._add(new Constraints.Parallel(origEdge, segment));
-        this.viewer.parametricManager._add(new Constraints.P2LDistanceSigned(a, segment.b, segment.a, delta));
+        pm._add(new Constraints.Parallel(origEdge, segment));
+        pm._add(new Constraints.P2LDistanceSigned(a, segment.b, segment.a, offsetConstant));
         edges.push(segment);
       } else if (origEdge._class == 'TCAD.TWO.Arc') {
         const connectionEdge = new SimpleEdge(new EndPoint(aOffX, aOffY), new EndPoint(bOffX, bOffY));
@@ -72,17 +73,17 @@ export class OffsetTool extends LoopPickTool {
           new EndPoint(origEdge.c.x + offVector.x, origEdge.c.y + offVector.y)
         );
         arc.stabilize(this.viewer);
-        this.viewer.parametricManager._linkObjects([arc.c, origEdge.c]);
-        this.viewer.parametricManager._add(new Constraints.RadiusOffset(inverse?arc:origEdge, inverse?origEdge:arc, delta));
+        pm._linkObjects([arc.c, origEdge.c]);
+        pm._add(new Constraints.RadiusOffset(inverse?arc:origEdge, inverse?origEdge:arc, offsetConstant));
         this.viewer.activeLayer.add(arc);
       }
     }
 
     for (let i = 0; i < edges.length; i++) {
-      this.viewer.parametricManager._linkObjects([edges[i].b, edges[(i + 1) % edges.length].a]);
+      pm._linkObjects([edges[i].b, edges[(i + 1) % edges.length].a]);
     }
-    this.viewer.parametricManager.solve(undefined, undefined, loopEdges);
-    this.viewer.parametricManager.refresh();
+    pm.solve(undefined, undefined, loopEdges);
+    pm.refresh();
     this.viewer.toolManager.releaseControl();
   }
   
@@ -124,4 +125,14 @@ function findLowestPoint(poly) {
     }
   }  
   return hero;
+}
+
+function createOffsetConstant(pm, value) {
+  let constant;
+  let i = 0;
+  do {
+    constant = 'OFFSET' + i++;
+  } while (pm.constantTable[constant]);
+  pm.defineNewConstant(constant, value);
+  return constant;
 }
\ No newline at end of file