In the Latin rite Catholic Church (I'll talk briefly about Western Rite Orthodox and others below) at the moment there are two main calendars that are currently approved for use, namely that for the Traditional Latin Mass/Extraordinary Form (EF), or 1960 rubrics Mass and Office, and that for the Ordinary Form/Novus Ordo (OF).
There are though a number of legitimate variants of these two basic calendars. Firstly every region, country, diocese, monastery and parish has particular local feasts that need to be added in to whatever 'universal' calendar you are using (such as their patronal feasts).
Secondly, each religious order (and in the case of Benedictines, Congregation and/or monastery) tends to customize its calendar to some degree, adding or subtracting particular saints and other variations.
The Farnborough Diurnal
The Farnborough Diurnal is based around the approved universal Benedictine Calendar aligned to the Extraordinary Form of the Mass. The dates for Easter and other moveable feasts etc are given in the introductory material, and you can sit down and work out an Ordo from what is contained in it.
And that's the Ordo I'm basically posting on this blog. Using it is the simplest (but not only) option for those using the Diurnal.
It fits well with the EF, because the saints feasts are more or less the same dates (with a few minor variances) and the I Vespers of Saturday/Sunday canticle antiphons, as well as the collect are generally identical to those used in the EF Mass and the Roman Breviary (and typically reflect the Matins Scriptural readings and Sunday Gospel).
Adapting to other calendars
You can of course use the traditional calendar even if you attend an Ordinary Form mass - most of the time it is just that the antiphons and collects won't align with the three year lectionary. And you will run into a few extra liturgical seasons (such as Septuagint) that have been abolished in the OF calendar.
But you could easily choose to celebrate the saints feasts of the new calendar or your particular monastery using the Farnborough Diurnal - just look them up in the book to align dates, and use the Common of the relevant type of saints for newer ones.
There are however a few other Ordos around that you should be aware of, at the very least to avoid confusion with them.
Firstly, some of the traditional monateries put out Ordos publically - Le Barroux for example puts theirs online. These are very useful guides, but each of these has some quirks perfectly legitimate for that monastery and its oblates to use, but perhaps problematic for others! Le Barroux for example still has I Vespers for class II feasts, which isn't in line with the universal 1962 rubrics, and adds in a lot of Roman EF feasts. Clear Creek and Fontgambault I think use a hybrid of the OF and EF calendars.
Secondly, there are Anglican Diurnals/Breviaries around. They typically add in a few feasts for non-Catholic approved saints (St King Charles I for example), and may use the pre-1960 calendar. An Ordo based on that is published by St Lawrence Press. Once again they publish some interesting and useful material on the liturgy, but this is not a currently approved catholic calendar.
Thirdly, there is a Monastic Diurnal published by Lancelot-St Andrewes Press, and an associated Ordo based around the Western Rite Orthodox calendar. Their website has some very useful materials on it but beware - Orthodox Easter is not the same date as Roman Rite, so using that calendar will lead to endless confusion if you are actually a Catholic rather than Orthodox...
Finally, there are some Ordos for the traditional Roman Breviary around - but the Benedictine Ordo is actually different to this in a number of respects.
Key point summary
- The Diurnal broadly follows the structure of the 1960 Extraordinary Form calendar, with adjustments for the Benedictine Confederation;
- But can be adapted to use with other calendars.