Tree ring density (signal-to-noise ratio ~15/1) and both high- and low-field magnetic susceptibility (susceptibility record has signal-to-noise ratio ~12/1 based on repetitive measurements) are plotted as a function of age. Top of the diagram shows intervals for the Medieval Warm Epoch period  and for Little Ice Age . The data are approximated with Stineman function. The output of this function then has a geometric weight applied to the current point and ± 10% of the data range, to arrive at the smoothed curve. This measurement was done at GSFC/NASA.