A computer based word processor or text editor is provided with a technique for defining line unit spacing which is particularly useful in a multi-font environment. A pop-down panel showing a miniature vertical scale line is displayed for the user. Adjacent the scale line is a handle which the user can select with a cursor. When the handle is selected, it may be moved up or down the scale line to the desired line unit spacing, at which time the handle is deselected. A numeric display of line unit spacing is also provided, and this display is continuously updated as the handle is moved. If the handle is moved to the top or bottom of the scale line, the scale line is moved up or down.