enum class mean_type : unsigned char  {

    arithmetic = 1, // sum(value) / count
    weighted = 2,   // sum(weighted value) / ((count * (count + 1)) / 2)
    geometric = 3,  // exp(log(sum(value)) / count)
    harmonic = 4,   // count / sum(1 / value)
    quadratic = 5,  // sqrt(sum(value * value) / count)
};