That was not a good example .
I have not narrowed down the exact tolerence but
pnt1, pnt2 will print duplicates and pnt3 will print non-duplicate
[CommandMethod("TestDupslicate")]
public void TestDupslicate()
{
Document doc = Application.DocumentManager.MdiActiveDocument;
Database db = doc.Database;
Editor ed = doc.Editor;
Point3dCollection pntcoll = new Point3dCollection();
Point3d pnt1 = new Point3d(4.000001, 7.000000001, 9.000000000000001);
pntcoll.Add(pnt1);
Point3d pnt2 = new Point3d(4.000001, 7.000000001, 9.00000000000001);
pntcoll.Add(pnt2);
Point3d pnt3 = new Point3d(4.000001, 7.000000001, 9.000000001);
pntcoll.Add(pnt3);
Point3d pnt4 = new Point3d(4.000001, 7.000000001, 9.0000000001);
foreach (Point3d pnt in pntcoll)
{
if (pnt.Equals(pnt4))
{
ed.WriteMessage("\nDuplicate");
}
else
{
ed.WriteMessage("\nNon-Duplicate");
}
}
}