How to use sacramentaries?

Hello - I’m at a loss about how one would use a sacramentary. If you’re a priest and in possession of a sacramentary, what would you do next?

More specifically: I’m browsing through this old sacramentary (early medieval style) where it says the UD (uere dignum) everywhere. Yet still, the vere dignum is supposedly only at the introduction of the Canon of the Mass, so why is it everywhere?

Any answer is welcomed - even from those who would admit that they too don’t understand it, as it would make me feel less as an imbecile :slight_smile:

The sacramentary is mostly for the preist to read from while celebrating Mass. It has the Eucharistic prayers, their prefaces, other prayers, etc.

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