How to print graphs at very high quality

In File->Print Preview… you can decide how detailed you want the graphs to be printed. The setting below is the default

The Detail property controls how screen pixels are mapped to printer pixels. By default it is set to Normal, meaning screen proportions will be respected when printing (Normal represents the Screen resolution printing 'What you See').

The closer the slider is moved left towards More, the higher the resolution of screen pixels passed to the printer.

The method is similar if you are using File->Print Preview All…, but in this dialog box, the Detail Level layout is somewhat different and its value is stored.