ETA difference

[littlejet]

Aircraft is 747 - 400
Sometimes there is a +/- 1 min difference between next waypoint ETA on the ND with DATA selected and next waypoint ETA on the RTE DATA, FMS page.
Does somebody know the reason?
Thnx

[CONF iture]

I assume ND ETA only takes account of present GS, when FMS ETA includes inserted forcast winds and temps.
The further the waypoint, the bigger chance a difference between both ETA.