Entering NATS tracks on the FMC

[Guest Celt]

I'm not sure if I've asked this before, so apologies, but when entering NATS tracks in teh FMC on teh 747-400 I notice a couple of oddities . . . firstly I was under the impression from the 737NG that the format for a lat/long waypoint was NXXXXXWXXXXXX e.g. N53000W050000 for a NAT waypoint of 53N050W , however the FMC doesn't accept this, but it will accept N53W050 . . . OK the next NAT waypoint is N54W040, which goes in but the FMC displays N54W039 the next is N54W030 which goes in OK, but the next one N54W020 comes up again as N54W019 ???????!!!?Now getting out my slide rule it appears that the waypoints are being placed correctly (because the distance between them is correct) but are being displayed wrong. I presume the data entry issue is a difference between the 737 FMC and the 747 FMC (correct me if I'm wrong) . . . but is the display error a bug?

[Guest Hawkeyeted]

Chris,You are correct on both accounts. The correct lat/long entry is as you described. The only explaination I have for the incorrect long. display (W039 vice W040) has got to be a mathmatical error of some sort (i.e. appearance to round up or down). I have replicated this numerous times, but was able to determine it was flying to the correct long (W040 vice W039 by checking against "shift-z").