All you need is to calculate the standard deviation?

I feel like I am missing something but here you go

Code:
        public static float LatchTimeStdev()
        {
            float sum = 0.0f ;
            float mean = LatchTimeMean();
            for (int i = 0; i < m_ValveResults.Count; i++)
            {
                float val = (mean - m_ValveResults[i].LatchTime);
                 sum += val * val;
            }
            return (float)Math.Sqrt(sum / (m_ValveResults.Count - 1));
        }