diff --git a/Makefile b/Makefile
index 2e87512a0..17ad73eb7 100644
--- a/Makefile
+++ b/Makefile
@@ -527,6 +527,9 @@ install-doxydoc: doxydoc
 	rsync -r -z --progress --delete doxydoc $(SF_WEB)
 
 
+doc/Ravel/labels.pl: $(wildcard doc/*.tex)
+	cd doc; sh makedoc.sh
+
 # upload manual to SF
 install-manual: doc/Ravel/labels.pl
 	rsync -r -z --progress --delete doc/minsky.html doc/Ravel $(SF_WEB)/manual
diff --git a/doc/Ravel.pdf b/doc/Ravel.pdf
index 36e5b8a02..9b98244a8 100644
Binary files a/doc/Ravel.pdf and b/doc/Ravel.pdf differ
diff --git a/engine/equations.cc b/engine/equations.cc
index 4e843883c..8ce54e223 100644
--- a/engine/equations.cc
+++ b/engine/equations.cc
@@ -515,7 +515,7 @@ namespace MathDAG
                          // try again later
                          integralInputs.emplace_back(input,i->ports(1).lock()->wires()[0]);
                          // clear error indicator
-                         minsky::minsky().canvas.itemIndicator=false;
+                         minsky::minsky().canvas.itemIndicator.reset();
                        }
                    }
                 
diff --git a/gui-js/apps/minsky-electron/src/app/managers/CommandsManager.ts b/gui-js/apps/minsky-electron/src/app/managers/CommandsManager.ts
index 3df6340a9..eb627d0b1 100644
--- a/gui-js/apps/minsky-electron/src/app/managers/CommandsManager.ts
+++ b/gui-js/apps/minsky-electron/src/app/managers/CommandsManager.ts
@@ -347,11 +347,10 @@ export class CommandsManager {
         Math.abs(itemX - 0.5 * canvasWidth) > 0.5 * canvasWidth ||
         Math.abs(itemY - 0.5 * canvasHeight) > 0.5 * canvasHeight
       ) {
-        const posX = itemX - (await minsky.canvas.item.x()) + 0.5 * canvasWidth;
-        const posY = itemY - (await minsky.canvas.item.y()) + 0.5 * canvasHeight;
+        const posX = itemX - (await minsky.canvas.itemIndicator.x()) + 0.5 * canvasWidth;
+        const posY = itemY - (await minsky.canvas.itemIndicator.y()) + 0.5 * canvasHeight;
         minsky.canvas.moveTo(posX,posY);
       }
-      minsky.canvas.itemIndicator(true);
       minsky.canvas.requestRedraw();
       WindowManager.getMainWindow()?.webContents?.send(events.RESET_SCROLL);
     } else {
diff --git a/gui-js/libs/shared/src/lib/backend/minsky.ts b/gui-js/libs/shared/src/lib/backend/minsky.ts
index 9499f2bc9..219157106 100644
--- a/gui-js/libs/shared/src/lib/backend/minsky.ts
+++ b/gui-js/libs/shared/src/lib/backend/minsky.ts
@@ -414,6 +414,7 @@ export class Canvas extends RenderNativeWindow {
   backgroundColour: ecolab__cairo__Colour;
   item: Item;
   itemFocus: Item;
+  itemIndicator: Item;
   lasso: LassoBox;
   model: Group;
   selection: Selection;
@@ -428,6 +429,7 @@ export class Canvas extends RenderNativeWindow {
     this.backgroundColour=new ecolab__cairo__Colour(this.$prefix()+'.backgroundColour');
     this.item=new Item(this.$prefix()+'.item');
     this.itemFocus=new Item(this.$prefix()+'.itemFocus');
+    this.itemIndicator=new Item(this.$prefix()+'.itemIndicator');
     this.lasso=new LassoBox(this.$prefix()+'.lasso');
     this.model=new Group(this.$prefix()+'.model');
     this.selection=new Selection(this.$prefix()+'.selection');
@@ -468,7 +470,6 @@ export class Canvas extends RenderNativeWindow {
   async hasScrollBars(): Promise<boolean> {return this.$callMethod('hasScrollBars');}
   async init(): Promise<void> {return this.$callMethod('init');}
   async itemAt(a1: number,a2: number): Promise<object> {return this.$callMethod('itemAt',a1,a2);}
-  async itemIndicator(...args: boolean[]): Promise<boolean> {return this.$callMethod('itemIndicator',...args);}
   async keyPress(a1: minsky__EventInterface__KeyPressArgs): Promise<boolean> {return this.$callMethod('keyPress',a1);}
   async lassoMode(...args: string[]): Promise<string> {return this.$callMethod('lassoMode',...args);}
   async lockRavelsInSelection(): Promise<void> {return this.$callMethod('lockRavelsInSelection');}
diff --git a/gui-js/package-lock.json b/gui-js/package-lock.json
index d7116af3c..7dadfac2f 100644
--- a/gui-js/package-lock.json
+++ b/gui-js/package-lock.json
@@ -32444,9 +32444,9 @@
       }
     },
     "node_modules/ws": {
-      "version": "8.17.0",
-      "resolved": "https://registry.npmjs.org/ws/-/ws-8.17.0.tgz",
-      "integrity": "sha512-uJq6108EgZMAl20KagGkzCKfMEjxmKvZHG7Tlq0Z6nOky7YF7aq4mOx6xK8TJ/i1LeK4Qus7INktacctDgY8Ow==",
+      "version": "8.17.1",
+      "resolved": "https://registry.npmjs.org/ws/-/ws-8.17.1.tgz",
+      "integrity": "sha512-6XQFvXTkbfUOZOKKILFG1PDK2NDQs4azKQl26T0YS5CxqWLgXajbPZ+h4gZekJyRqFU8pvnbAbbs/3TgRPy+GQ==",
       "engines": {
         "node": ">=10.0.0"
       },
diff --git a/model/canvas.cc b/model/canvas.cc
index c1abd1498..c6c9245cb 100644
--- a/model/canvas.cc
+++ b/model/canvas.cc
@@ -185,7 +185,7 @@ namespace minsky
     lassoMode=LassoMode::none;
 
     
-    itemIndicator=false;
+    itemIndicator.reset();
     rotatingItem=false;
     itemFocus.reset();
     wireFocus.reset();
@@ -776,7 +776,7 @@ namespace minsky
             iv->type()==VariableType::parameter || iv->inputWired())
           return true;
         
-        auto def=model->findAny
+        itemIndicator=model->findAny
           (&GroupItems::items, [&](const ItemPtr& i) {
             if (auto v=i->variableCast())
               return v->inputWired() && v->valueId()==iv->valueId();
@@ -790,9 +790,7 @@ namespace minsky
               return o->intVar->valueId()==iv->valueId();
             return false;
           });
-        if (def)
-          item=def;
-        return def.get();
+        return itemIndicator.get();
       }
     return false;
   }
@@ -852,7 +850,14 @@ namespace minsky
              const CairoSave cs(cairo);
              cairo_identity_matrix(cairo);
              cairo_translate(cairo,it.x(), it.y());
-             it.draw(cairo);
+             try
+               {
+                 it.draw(cairo);
+               }
+             catch (const std::exception& ex)
+               {
+                 cerr << ex.what() << endl;
+               }
            }
          return false;
        });
@@ -910,11 +915,11 @@ namespace minsky
         cairo_stroke(cairo);
       }
 
-    if (itemIndicator && item) // draw a red circle to indicate an error or other marker
+    if (itemIndicator) // draw a red circle to indicate an error or other marker
       {
         const CairoSave cs(surface()->cairo());
         cairo_set_source_rgb(surface()->cairo(),1,0,0);
-        cairo_arc(surface()->cairo(),item->x(),item->y(),15,0,2*M_PI);
+        cairo_arc(surface()->cairo(),itemIndicator->x(),itemIndicator->y(),15,0,2*M_PI);
         cairo_stroke(surface()->cairo());
       }
 
diff --git a/model/canvas.h b/model/canvas.h
index c894a639f..4ee6d620e 100644
--- a/model/canvas.h
+++ b/model/canvas.h
@@ -116,8 +116,8 @@ namespace minsky
       rotatingItem=true;
     }
     ClickType::Type clickType;
-    /// for drawing error indicators on the canvas
-    bool itemIndicator=false;
+    /// for drawing error indicator on the canvas
+    ItemPtr itemIndicator;
 
     /// lasso mode support
     struct LassoMode {enum type  {none, lasso, itemResize};};
diff --git a/model/minsky.cc b/model/minsky.cc
index 3b526ce38..a505c055f 100644
--- a/model/minsky.cc
+++ b/model/minsky.cc
@@ -888,7 +888,7 @@ namespace minsky
 
         auto start=chrono::high_resolution_clock::now();
         auto updateResetDuration=onStackExit([&]{resetDuration=chrono::duration_cast<chrono::milliseconds>(chrono::high_resolution_clock::now()-start);});
-        canvas.itemIndicator=false;
+        canvas.itemIndicator.reset();
         const BusyCursor busy(*this);
         EvalOpBase::t=t=t0;
         lastT=t0;
@@ -1249,26 +1249,24 @@ namespace minsky
     // this method is logically const, but because of the way
     // canvas rendering is done, canvas state needs updating
     auto& canvas=const_cast<Canvas&>(this->canvas);
-    canvas.item=nullptr;
     if (op.visible())
-      canvas.item=canvas.model->findItem(op);
+      canvas.itemIndicator=canvas.model->findItem(op);
     else if (auto v=op.variableCast())
       if (auto c=v->controller.lock())
         displayErrorItem(*c);
 
-    if (!canvas.item)
+    if (!canvas.itemIndicator)
       if (auto g=op.group.lock())
         {
           while (g && !g->visible()) g=g->group.lock();
           if (g && g->visible())
-            canvas.item=g;
+            canvas.itemIndicator=g;
         }
     
-    canvas.itemIndicator=canvas.item.get();
     if (canvas.item)
       {
-        auto physX=canvas.item->x();
-        auto physY=canvas.item->y();
+        auto physX=canvas.itemIndicator->x();
+        auto physY=canvas.itemIndicator->y();
         if (physX<100 || physX>canvas.frameArgs().childWidth-100 ||
             physY<100 || physY>canvas.frameArgs().childHeight-100)
           {
diff --git a/model/variable.cc b/model/variable.cc
index e169d058c..bf455075e 100644
--- a/model/variable.cc
+++ b/model/variable.cc
@@ -168,7 +168,11 @@ shared_ptr<VariableValue> VariableBase::vValue() const
 
 vector<unsigned> VariableBase::dims() const
 {
-  if (auto v=vValue()) return v->hypercube().dims();
+  try
+    {
+      if (auto v=vValue()) return v->hypercube().dims();
+    }
+  catch (...) {} // ignore any exceptions caused by evaluating RHS.
   return {};
 }
     
@@ -324,8 +328,12 @@ string VariableBase::init(const string& x)
 
 double VariableBase::value() const
 {
-  if (isValueId(valueId()))
-    return minsky::cminsky().variableValues[valueId()]->value();
+  try
+    {
+      if (isValueId(valueId()))
+        return minsky::cminsky().variableValues[valueId()]->value();
+    }
+  catch (...) {} // ignore any errors in RHS
   return 0;
 }
 
@@ -696,6 +704,7 @@ void VariableBase::draw(cairo_t *cairo) const
 
       auto vv=vValue();
       if (miniPlot && vv && vv->size()==1)
+        try
         {
           if (cachedTime!=cminsky().t)
             {
@@ -707,56 +716,59 @@ void VariableBase::draw(cairo_t *cairo) const
           cairo_translate(cairo,-w,-h);
           miniPlot->draw(cairo,2*w,2*h);
         }
-  
+        catch (...) {} // ignore errors in obtaining values
+
       // For feature 47
-      if (type()!=constant && !ioVar() && vv && vv->size()==1 && vv->idxInRange())
-        try
-          {
-            if (!cachedMantissa || cachedMantissa->cairoContext()!=cairo)
-              {
-                cachedMantissa=make_shared<Pango>(cairo);
-                cachedMantissa->setFontSize(6.0);
-                cachedExponent=make_shared<Pango>(cairo);
-                cachedExponent->setFontSize(6.0);
-                cachedValue=nan("");
-              }
-          
-            auto val=engExp();    
-            if (value()!=cachedValue)
-              {
-                cachedValue=value();
-                if (!isnan(value())) {
-                  if (sliderBoundsSet && vv->sliderVisible)
-                    cachedMantissa->setMarkup
-                      (mantissa(val,
-                                int(1+
-                                    (sliderStepRel?
-                                     -log10(maxSliderSteps()):
-                                     log10(value()/maxSliderSteps())
-                                     ))));
-                  else
-                    cachedMantissa->setMarkup(mantissa(val));
+      try
+        {
+          if (type()!=constant && !ioVar() && vv && vv->size()==1 && vv->idxInRange())
+            {
+              if (!cachedMantissa || cachedMantissa->cairoContext()!=cairo)
+                {
+                  cachedMantissa=make_shared<Pango>(cairo);
+                  cachedMantissa->setFontSize(6.0);
+                  cachedExponent=make_shared<Pango>(cairo);
+                  cachedExponent->setFontSize(6.0);
+                  cachedValue=nan("");
                 }
-                else if (isinf(value())) { // Display non-zero divide by zero as infinity. For ticket 1155
-                  if (signbit(value())) cachedMantissa->setMarkup("-∞");
-                  else cachedMantissa->setMarkup("∞");
+          
+              auto val=engExp();    
+              if (value()!=cachedValue)
+                {
+                  cachedValue=value();
+                  if (!isnan(value())) {
+                    if (sliderBoundsSet && vv->sliderVisible)
+                      cachedMantissa->setMarkup
+                        (mantissa(val,
+                                  int(1+
+                                      (sliderStepRel?
+                                       -log10(maxSliderSteps()):
+                                       log10(value()/maxSliderSteps())
+                                       ))));
+                    else
+                      cachedMantissa->setMarkup(mantissa(val));
+                  }
+                  else if (isinf(value())) { // Display non-zero divide by zero as infinity. For ticket 1155
+                    if (signbit(value())) cachedMantissa->setMarkup("-∞");
+                    else cachedMantissa->setMarkup("∞");
+                  }
+                  else // Display all other NaN cases as ???. For ticket 1155
+                    cachedMantissa->setMarkup("???");
+                  cachedExponent->setMarkup(expMultiplier(val.engExp));
                 }
-                else // Display all other NaN cases as ???. For ticket 1155
-                  cachedMantissa->setMarkup("???");
-                cachedExponent->setMarkup(expMultiplier(val.engExp));
-              }
-            cachedMantissa->angle=angle+(flipped? M_PI:0);
+              cachedMantissa->angle=angle+(flipped? M_PI:0);
             
-            cairo_move_to(cairo,r.x(w-cachedMantissa->width()-2,-h-hoffs+2),
-                          r.y(w-cachedMantissa->width()-2,-h-hoffs+2));
-            cachedMantissa->show();
+              cairo_move_to(cairo,r.x(w-cachedMantissa->width()-2,-h-hoffs+2),
+                            r.y(w-cachedMantissa->width()-2,-h-hoffs+2));
+              cachedMantissa->show();
 
-            if (val.engExp!=0 && !isnan(value())) // Avoid large exponential number in variable value display. For ticket 1155
-              {
-                cairo_move_to(cairo,r.x(w-cachedExponent->width()-2,0),r.y(w-cachedExponent->width()-2,0));
-                cachedExponent->show();
-              }
-          }
+              if (val.engExp!=0 && !isnan(value())) // Avoid large exponential number in variable value display. For ticket 1155
+                {
+                  cairo_move_to(cairo,r.x(w-cachedExponent->width()-2,0),r.y(w-cachedExponent->width()-2,0));
+                  cachedExponent->show();
+                }
+            }
+        }
         catch (...) {} // ignore errors in obtaining values
 
       {
diff --git a/obsCheck/Dockerfile-tumbleweed b/obsCheck/Dockerfile-tumbleweed
index 61af3b65e..a8ac1d0cb 100644
--- a/obsCheck/Dockerfile-tumbleweed
+++ b/obsCheck/Dockerfile-tumbleweed
@@ -3,7 +3,7 @@ ARG project=minsky
 ADD . /root
 RUN zypper addrepo https://download.opensuse.org/repositories/home:hpcoder1/openSUSE_Tumbleweed/home:hpcoder1.repo
 RUN zypper --gpg-auto-import-keys refresh
-RUN zypper --non-interactive install $project
+RUN zypper --non-interactive install $project python3
 RUN useradd -m minsky
 RUN su - minsky -c minsky --version
 RUN python3 -c "import pyminsky"