Our rad alt had 2 scales, 0 to 500 for low level work, great for night EOLS!. 0 to 5000 to make sure you were above 3000 to be safe from small arms fire. You just pushed a button I think to change the scale. The bug was set in the usual way. A very accurate rad alt as we did EOLS without looking out, just did it on the rad alt.