All the above suggestions achieve the TOD calculation simply.
For my halfpenny's worth, I use all the same calcs but disregard the additional 10 miles for slowing down at 10,000ft/ lowering flaps, slats and gear. I gain the 10 miles by increasing the RoD in the early part of the descent (where there is less drag and higher TAS), and then reduce RoD and IAS as I get into the lower and denser air at say 15,000ft.
If you descend at 2,500-3,000fpm from top of drop (above FL350) till you reach FL150 then decrease the RoD to 1,500 fpm without changing power, everything works out beautifully for a constant power approach.