convert an AD age scale to BP

a ggplot scale to convert a BP axis to AD

AD2BP_trans()

See also

Other plot help: BP2AD_trans(), axisLabel(), bin2d(), geoChronRPlotTheme(), getLegend(), getPlotRanges(), kde2d(), meltDistributionTable(), modeSelektor(), periodAnnotate(), quantile2d(), reverselog10_trans()