This applies to the 330 - 200. Don't know how much different the 330 - 300 is.
Look at your ground speed over 10 and subtract 15. To that add 3 times the altitude in thousands.
This provides a dynamic and reasonably accurate check on an uninterrupted (ie ATC modified) descent profile from TOD to around 5000 ft, before configuring for landing.
Example. GS 480, FL 380.
480/10 - 15 = 33.
3 x 38 = 114.
Distance = 33 + 114 = 147 NM.
Performing this calculation frequently on descent should confirm the accuracy.
