It is simply a variation on the normal Rate of Descent formula so there's hardly anything new or extra to remember.

On a 3 degree Glide Path

Change of Rate of Descent = Change of Ground Speed x 5

CRoD = -30 x 5 = -150

(You will only be questioned at 3 degrees)

However, on other Glide Paths

CRoD = Change GS x 5 x (GP/3)