1 Each Yi is obtained by repeatedly generating a random distance Yij with its corresponding probability Z(Yij) , and a random number Rj (0 <= Rj <= 1/sigmasqrt(2pi)) until the first occurrence of Z(Yij) >= Rj, which indicates an acceptable Yi. As the distribution of all Yi builds up, the tails rapidly become fixed and the `bell' gets taller, but relative areas under the graph remain the same (e.g. 95% of the area lies within ±1.96sigma).