Fig. 3

A normal distribution curve has been used to divide circular two-dimensional dot-plots into six zones. Normal distribution curve for circular two-dimensional dot-plots is divided into six zones as follows from the left: “-t zone” < −3σ, 3σ≦ “-d zone” < −1σ, −1σ≦ “-s zone” < 0, 0 < “s zone” ≦ + 1σ, +1σ < “d zone” ≦ + 3σ, 3σ < “t zone”