DIALOG UNITS

Dialog box and control dimensions and coordinates are device-independent. Because a dialog box may be displayed on system displays that have widely varying pixel resolutions, dialog box dimensions are specified in system-character widths and heights instead of pixels.  

This helps to ensure the best possible appearance of characters in the dialog, and enables dialog boxes to appear with similar proportions and appearance on the screen, even when the resolution and aspect ratio can significantly vary.

The dialog box base units are computed from the height and width of the system font. As the display resolution is changed, Windows changes the system font size accordingly, thereby adjusting the dialog unit size proportionally to the resolution.  

By default, the actual font used in PowerBASIC's Dynamic Dialog Tools (DDT) dialogs is 8 point "MS Sans Serif". When designing your dialogs, it is a good idea to make controls slightly wider and taller than the text label size. This additional tolerance helps to ensure that the text is not clipped if the default dialog font is slightly larger in some resolutions. You can also use the DIALOG FONT statement to specify a custom default DDT font.  

You can convert between Dialog Units and Pixels with the built in DIALOG PIXELS and DIALOG UNITS statements.