OW5 is correct in that in the early days of scale modeling in the US there were two scales used for scale O. One was 1/4" to the foot which makes the track spacing too wide. The other scale was 17/64" which allows for the correct spacing of 4'-8-1/2" between the rails. Ultimately 1/4" to the foot won out in the US, but models were still produced in 17/64 up into the early 50's. In Europe and the UK they use the correct scale at 1:43.5 whereas 1/4" to the foot is 1:48.
You are also correct in the use of "W" for wide gauge and "N" for narrow gauge. The Erie started life at 6' scale track which made the change to standard gauge 1:1 easy as they had the width for it. The former Soviet Union used wide gauge on a number of lines as well. The last number represents track spacing. Most common size was 3' gauge in the western US, but there are still some active 2' gauge lines throughout the world.
IPA is India Pale Ale. A requirement for operating sessions. 
