I'm trying to understand principles of solidworks API, but have several problems. Here is my code:

for (var i = 0; i < selMgr.GetSelectedObjectCount(); i++) {
 var Face = selMgr.GetSelectedObject(i+1);
 surfaces.Add(Face.GetSurface());
 measure = swModel.Extension.CreateMeasure();
  if (surfaces[i].IsCylinder()) {

  // Problem # 1  

     Console.WriteLine("Cylinder " + i);
     measure.Calculate(surfaces[i]);

     var diameter = measure.Diameter * 1000; 
     var length = 1000 * measure.Perimeter  / (measure.Diameter * Math.PI);  
     var temp = swApp.OpenDoc6(@"E:\\OAK\\Locator9.SLDPRT", 1, 1, "", 0, 0); 
     var part = component.AddComponent5(@"E:\\OAK\\Locator9.SLDPRT", 0, "", true, "", 0, 0, 0.3); 
     swApp.CloseDoc(@"E:\\OAK\\Locator9.SLDPRT");  
     ModelDoc2 locator = part.GetModelDoc();  
     var eqMgr = locator.GetEquationMgr();  

     Console.WriteLine("Evaluated diameter " + diameter); 
     Console.WriteLine("Evaluated length " + length);  
     Console.WriteLine(eqMgr.Equation[1] + "   " + eqMgr.Equation[2]);  

     //Problem #2   

     eqMgr.set_Equation(1, \\\$@"""D""={diameter}"); 
     eqMgr.set_Equation(2, \\\$@"""L""={length}"); 
     eqMgr.EvaluateAll(); locator.EditRebuild3(); 
     locator.ForceRebuild3(false); 
     } else { // TODO: Handle other type of surface  } }

1) I want to measure perimeter & diameter of the selected surface. But if a return value of GetSelectedObjectCount() method is greater than 1, measure.Diameter & measure.Perimete  both returns -1 .And I kinda understand why, 'cause such operation isn't possible via UI as well (at least with my experience), but can I do smth to solve the problem?
2) The code above has no influence on the equation of the inserted component, even if it writes it on the console. Help please!