Oh...So that would only apply for a fare between, say, Llanfair P.G. and Penmaenmawr, then? Sorry, I thought it applied to all journeys!
To get associated routeing points for a station you use section B - the pink pages.
Let's take an example local to you - Aldershot to Basingstoke. Basingstoke is itself a routeing point (confirmed in section B), and the appropriate routeing points for Aldershot are Ash Vale, Farnborough Group, and Guildford.
The fares to check (using the same ticket type each time) are, therefore:
Aldershot to Basingstoke (the journey being undertaken), Ash Vale to Basingstoke (origin routeing point 1), Farnborough* to Basingstoke (origin routeing point 2), and Guildford to Basingstoke (origin routeing point 3). If any of the three last ones are more expensive than the first that routeing point cannot be used.
*If it makes a difference (e.g. if there is no 'stations' fare used for that journey) I go by the rule of using the main station in a group to check fares for - e.g. in Southampton Group I always use Central to make comparisons (not that it often makes too much difference though!).
We see, looking at Avantix, that the valid routeing points for Aldershot are Ash Vale and Farnborough (Guildford to Basingstoke is more expensive than Aldershot to Basingstoke). So we then look at Section C - the yellow pages - to see which maps Ash Vale to Basingstoke and Farnborough to Basingstoke are valid by and use those maps to find valid routeings (without passing through Guildford or the same station more than once unless an easement allows it).
Aldershot to Ash Vale/Farnborough must be undertaken using the shortest route as per the instructions.
In cases where there are more than one associated routeing point for each the origin and destination more fares chacking has to take place:
e.g. Acle to Adderley Park (picking an easy one at random!)
Acle is associated to Ipswich and Norwich, Adderley Park to Birmingham Group and Coventry.
Fares to check here would be:
Acle to Adderley Park (the journey being undertaken), Ipswich to Adderley Park (origin routeing point 1), Norwich to Adderley Park (origin routeing point 2), Acle to Birmingham (destination routeing point 1), and Acle to Coventry (destination routeing point 2) - i.e. every permutation of origin routeing points with the destination, and destination routeing points with the origin.
Any of the last four that are greater than the first will reject routeing point options.
Just to give me a starting point for understanding exactly how the NRRG permits routes though - Including illogical ones like this - Can I ask what the main points of this route are?
Is it just because EXD and BRI both appear on maps WR and WX, or is there something else that also reinforces that?
When changing between maps all that you are looking for is a common station on both maps - it can be any provided you are not doubling back (passing through a station more than once) or passing through a fare-check-forbidden routeing point (unless an easement says you can).
Also...Don't the maps have to be used in the order listed on their entries in the yellow pages? If so, WR+WX might only be valid for SLO > WOK and not the other way around (Which would require WX+WR)... :?
Maps can be used either in the quoted order or the reverse of the quoted order. The order cannot otherwise be changed and no map can be skipped or added. WX+WR is, in essence, the same as WR+WX,
but WX+PD+SC is
not the same as WX+SC, WX+WR+PD+SC, or PD+WX+SC for instance.
Dear Gods...I thought that operating a Ferranti Pegasus using six-bit instructions and binary I/O was confusing enough! I'd say that he who understands the NRRG in full and can wield it like a Flaming Sword against RPOs really ought to apply for MENSA...

hock:
Probably for that reason that the routeing guide is often not taught on retail courses...
Finally: If it eventually looks like this working
is valid (And I do hope it is!

) I'm planning to use it myself. However to avoid the problems encountered by Embers25 I'd be planning on taking a printed copy of the NRRG as published by AToC themselves so that no Guards or RPOs could argue the legitimacy of the information that I'm using. Does anyone know where and how I can purchase an official copy of the NRRG, and if so how much is it?
You're already on the only official version of the guide. It is no longer printed (indeed the only printed version several years ago was rather limited edition...) and everybody who needs routeing information has to use those PDFs!!
If you end up in dispute, all you can do is ask them to check the Routeing Guide section in FRPP as mentioned above and let them see how for themselves... although with the complex issue of learning to use the thing don't expect them to be too willing to sit down for half an hour working if your routeing is permitted!
If they still won't play ball then ask them to call their customer services department (or do it yourself) and ask to speak to the fares/routeing manager and let them sort it out. Hopefully that is a decent thing to do and they'll assist you/their member of staff as best as possible.
Hope this helps, and if you're still having difficulty with the NRG then we'll try our best to help

.