Descending Distance & Rate of Descent (RoD) --
-- Top of Descent for Crossing Restriction
100 ft/min is approximately 1 knot. So to figure your glide ratio: ground speed
divided by VSI/100 (take 2 zeros off VSI).
example: Ground speed = 100 kts
VSI shows -500 ft/min -- Drop two zeros: 5 kts
100/5 = 20:1 glide ratio