From Xojo Documentation
Set to the maximum vertical resolution at which you wish to print. The default value is 72.
You can change it to the maximum printer resolution you're prepared to handle or -1 for the highest possible resolution of the output device. After calling ShowPageSetupDialog, OpenPrinter, or ShowPrinterDialog, the VerticalResolution property will automatically be set to the highest resolution supported by the printer driver, within your specified constraints, although this may be less than what you have specified. Printing occurs at VerticalResolution, so you should always check and use that value after setting this value.
This example sets the MaximumVerticalResolution and MaximumHorizontalResolution properties.