public ActionResult TankDuration(TankDurationViewModel input_model)
        {
            if (ModelState.IsValid)
            {
                try
                {
                    //Duration(in minutes) = (gauge_pressure(psi) * tank_factor) / liter_flow
                    EquationsRepository equationRespository = new EquationsRepository(Cache, ReadEquationData);
                    Equation requestedEquation = equationRespository.GetAnEquation("Tank_Oxygen_Duration");

                    if (requestedEquation != null)
                    {
                        string myEquationExpression = requestedEquation.EquationExpression;
                        double myAnswer = 0;
                        string error = string.Empty;

                        //Substitute my variable in equation with value from user.

                        myEquationExpression = myEquationExpression.Replace("tank_factor", input_model.selectedTankFactor.ToString());
                        myEquationExpression = myEquationExpression.Replace("gauge_pressure_psi", input_model.gauge_pressure_psi.ToString());
                        myEquationExpression = myEquationExpression.Replace("liter_flow_L", input_model.liter_flow_L.ToString());

                        if(MathExpressionParser.SolveExpression(myEquationExpression,out myAnswer,out error))
                        {
                            input_model.myAnswer = myAnswer;
                        }
                        else
                        {
                            myLogger.Error("Error using SimpleCalculatorService: "+ error);
                            return View("Error");
                        }
                        //DemoMVC.SimpleCalcServiceConsoleHost.CalculatorClient calculatorClient = new SimpleCalcServiceConsoleHost.CalculatorClient();

                        //try
                        //{
                        //    myAnswer = calculatorClient.SolveExpression(myEquationExpression);
                        //    input_model.myAnswer = double.Parse(myAnswer);
                        //    // More code that isn't useful including here ...

                        //}
                        //catch (Exception e)
                        //{
                        //    ErrorSignal.FromCurrentContext().Raise(e);
                        //    //logger.Error("Error using SimpleCalculatorService.", e);
                        //}
                        //finally
                        //{
                        //    calculatorClient.Close();
                        //}
                    }

                }
                catch (Exception ex)
                {
                    myLogger.Error("Error using SimpleCalculatorService: ",ex);
                    return View("Error");
                    //ErrorSignal.FromCurrentContext().Raise(ex);
                }
            }

            return View(input_model);
        }
        // GET: Respiratory
        public ActionResult TankDuration()
        {
            TankDurationViewModel model = new TankDurationViewModel();

            return View(model);
        }