  Graphical techniques are recommended for critical applications in order to
share information with non-statisticians, since they allow for a visual
analysis and helpful understanding of the results. However, graphical
estimation methods are often underestimated because of their minor efficiency
with respect to the analytical ones. Therefore, finding unbiased plotting
positions can contribute to rise their reputation and to encourage their
strategic use. This paper proposes a new general plotting position formula
which can be as close as needed to the exact unbiased plotting positions. The
ability of the new solution in estimating quantiles for both symmetrical and
skewed location-scale distributions is shown via Monte Carlo simulation. An
applicative example shows how the proposed formula enables to perform, with
known accuracy, the graphical analysis of critical data, such as the earthquake
magnitudes registered during the serious 1983-1984 bradyseismic crisis in Campi
Flegrei (Italy). Moreover, the proposed formula gives a unified look at
existing plotting positions and a definitive insight into plotting position
controversies recently renewed in the literature.
