Nesting example

Invert statement.cs

        public double RefDoingCalculations()
        {
            if (!_firstGuard)
            {
                return 0;
            }

            if (!_secondGuard)
            {
                return FirstCalculation();
            }

            if (!_thirdGuard)
            {
                return SecondCalculation();
            }

            return ThirdCalculation();
        }

Nesting.cs

        public double DoingCalculations()
        {
            var result = 0d;

            if (_firstGuard)
            {
               result = FirstCalculation();

                if (_secondGuard)
                {
                    result = SecondCalculation();

                    // 100 LOC ......
                }   
            } 

            return result;
        }