¹ Each Y_i is obtained by repeatedly generating a random distance Y_ij with its corresponding probability Z(Y_ij) , and a random number R_j (0 R_j 1/(2)) until the first occurrence of Z(Y_ij) R_j, which indicates an acceptable Y_i. As the distribution of all Y_i 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 ±1.96).