This is a time of the year when those of us who offer daily the August Sacrifice ... and /or say the Divine Office ... find our minds turning to the thought of Next Year's ORDO.
One really does need an ORDO to know what's going on liturgically, day by day.
Real traddies, using the Sarum Rite, needed to resort to PICA, of which Thomas Cranmer wrote "the nombre and hardnes of the rules called the pie and the manifold changings of the service, was the cause, that to turne the boke only, was so hard and intricate a matter, that many times, there was more busines to fynd out what should be read, then to read it when it was founde out."
Coming down to near-modernity: in the Good Old Days when the Roman Rite was endearingly complex, and the Ordo was in Latin, the one to get was one which still survives annually today, and which I very strongly commend: the Saint Lawrence Press Ordo [59 Sandscroft Avenue, Broadway, Worcestershire, WR12 7EJ]. There you found and still find the full glory of privileged octaves, common vigils, doubles of the Second Class, you name it, all just as it was before Bugnini's chum Eugenio Pacelli, sometimes known as Pius XII, started the long gruesome process still known by the gullible as 'Reform'. These were the days (1923) when Mgr Ronald Knox wrote a spoof review of " ... the unpretentious but tastefully produced booklet that reaches us from Burns, Oates, & Washbourne, entitled Ordo Recitandi Divini Officii, etc., (1/6 net). The author modestly preserves anonymity, nor does he betray his identity by any marked individuality of treatment; but his colleagues will be glad to welcome a piece of solid work from his pen, and will not fail to recognise his painstaking attention to detail and his terse, nervous Latinity ... "
In the C of E, we often used the Ordo of the nearest Popish diocese; thus one can work out that Eric Mascall's The Ultra Catholic (1959) probably lived within the geographical Archdiocese of Westminster: "The psalms of Dahvid I recite in heaven's own native Latin./And though I don't quite understand those awkward moods and tenses,/ My ordo recitandi's strict Westmonasteriensis." [The Wantage Sisters still produced up to 1969 an English ORDO " ... in strict accordance with the use of the Western Church."]
Back down to earth and the Novus Ordo: I still edit annually an Anglican ORDO; curiously, the calendars of readings currently guaranteed by the Authority of the General Synod are (I mean this seriously) very much more complex than Pie or anything in Sarum, so you do need a lectionary. The Ordinariate offers an extremely nice ORDO based upon the (much preferable) Anglican rules of 1961.
The Latin Mass Society provides a very neat (and recently reconfigured) ORDO for the 1962 rite. The SSPX ... I think ....
One thing to check: do you need an ORDO which provides for local Saints? If so, you should make sure you get an ORDO which does actually do this. It really does matter; around this time of the year, various dioceses prescribe(d) S Willibrord; S Justus; Holy Abbots Hugh Cook, Richard Whiting, and John Beche.
TODAY ... for example ... you wouldn't want to have missed S Edmund Rich, of Abendon, Oxford, and Canterbury, Patron of the Catholic diocese of Portsmouth ... would you?
Or ... in the next few days ... S Margaret of Scotland, S Hugh, S Hilda or S Edmund of Edmundsbury ...
The LMS ORDO does give all such local information; so does an American SSPX ORDO, which encompasses all the dioceses of the the entire Anglophone world.