R2001 Drawing Setup option documentation for: view_scale_format            

view_scale_format

decimal, fractional, ratio_colon

expresses a scale as a decimal or fractional value. if set to "ratio_colon," displays the view scale values as a ratio. for example, instead of a view scale of 0.5, displays the view scale as 1:2. since the ratio is just another way of displaying a fraction, make sure that you set the "view_scale_denominator" option appropriately.