TIME SCALE 515 to appear for selected intervals, such as Paleogene, Late Cretaceous, or Ordovician; these studies selected a small suite of radioisotopic dates with high internal analytical precision and relatively precise stratigraphic position At the same time, a high-resolution Neogene time-scale started to take shape, using orbital tuning of long sequences of sedimentary and/ or oxygen isotope cycles in the Mediterranean region and in Atlantic and Pacific pelagic sediments The present trend for the pre-Neogene is to incorporate radioisotopic dates that have very small analytical and stratigraphic uncertainties, and pass the most stringent tests The third step, interpolating the stratigraphic and radiometric information, has also evolved An early method had already constructed the basic two-way graph and was being used This graph plotted the cumulative sum of maximum thicknesses of strata in thousands of feet per stratigraphic unit along the vertical axis and selected dates from volcanic tuffs, glauconites, and magmatic intrusives along the horizontal linear axis This ‘best-fit’ line method, shown in Figure as it was used in 1960, incorporated an uncertainty envelope from the errors on the radioisotopic age constraints Despite its crudeness, the method was remarkably effective, but is a far cry from methods used today In the mid-1990s, Frits Agterberg and Felix Gradstein started to apply mathematical-statistical error analysis to the time-scale ages, which, for the first time, allowed them to assign fairly realistic error bars to ages of Mesozoic stage boundaries, a trend that persists today A simplified introduction to the modern building tools is presented the following discussions, but first consider a frequently asked question: ‘Which time-scale should be used?’ Which Time Scale Should Be Used? Of the several geological time-scales published in the past decade, a simple answer is to use the most recent one A better answer is to investigate the pros and cons of these time-scales, the improvements that a new one might bring to a study, and to remember that it is not desirable to change units of measurement during execution of an experiment or survey or basin modelling exercise