Oversampling, or scaling down

I think Tk will correctly honor the DPI by default, but ignore DPI if a font size is a negative value. I know this because years ago after a distro update tkdiff started to render at different sizes on my different-DPI monitors, rather than scaling to approximately the same size. I tracked it down to a "bugfix" where somebody changed the default font size to a negative size in order to work around situations where the DPI was set incorrectly (sigh).