/// <summary>式を検証し、結果を返す。</summary>
        /// <param name="formula"></param>
        /// <param name="formula_LastValid"></param>
        /// <param name="result"></param>
        /// <param name="isValid"></param>
        protected void ValidateFormula(string formula, string formula_LastValid, out double result, out bool isValid)
        {
            FormulaEngine engine = Application.FormulaEngine;

            isValid = true;
            try
            {
                result = engine.Calculate(formula);
            }
            catch (FormulaResultException)
            {
                isValid = false;
                result  = engine.Calculate(formula_LastValid);
            }
        }