If no wind is entered in the descent forecast page then will it work out on zero wind?
I always understood that if there are no descent winds entered, it works on the cruise wind washing out to zero during the descent. I find it generally calculates descents fairly well if you put the last cruise wind for the top one, a halfway down descent wind and altitudes in from the computer flight plan, and make the lowest wind 2000' and what is reported from the ground. BUT, the most important thing is you don't just sit there and rely on it- all the way down you should be mentally calculating and adjusting for the wind component. It's only a computer with all the faults of the programmers. YOU are flying the plane. The 757 tends to take you down too early, adjusting the wind to increase the tailwind components by about 10 kts works for that aeroplane. The 737NG sometimes has a real calculation 'burp' and can suddenly start telling you you are 7000' high on the profile descent. That is why it is important that YOU decide, and just don't leave it to a computer.