Visual Assist tells you when you have reached a desired line length with a column indicator. The indicator, common to non-Microsoft IDEs, appears at the trailing edge of the indicated column.
Select the location of the indicator and its color in the options dialog of Visual Assist.
Column indicators are available when using a fixed or proportional font in the text editor. For proportional fonts, the location of an indicator is determined by measuring multiple widths of the letter m.
If you want an indicator at three inches from the left margin and there are ten m characters per inch in your font, specify the indicator be placed after column 30.