is there anyway of telling what ratio a diff is when its in an axle?

im configuring my gear indicator, have the box ratios but not sure on the diff

thanks

You can do it by jacking up one wheel only and counting the turns ---- odds are unless your axle came from a Van or an 1100 or a 1600 or RS2000 it will be a 3.88:1 ratio as th vast majority of Escorts were 1300.