Some questions about Casting Tablets

How "large" is a casting tablet? Copying a tablet takes the same time as copying the lab text for the corresponding spell, so a fourth magnitude tablet should be, say, something of the order of (at least) several thousand words and maybe a dozen figures. But if that's the case, how can you cast from it in a single round? The reason I'm asking is to figure out how easy to carry a small collection of casting tablets might be, or how much space it would take if painted on walls or engraved on a floor.

Covenants states "A magus casting from a tablet ... may not tinker with decisions made by the author. The Range, Duration, and Target of the spell; the exact amount and Art of raw vis consumed; and any single type of arcane connection to be used, are specified by the author at writing". Hmm. Range, Duration and Target means e.g. T:Ind, not T:the lady Guinevre, right? And "type of arcane connection" means something like "this tablet can only be used with arcane connections lasting days", right?

Covenants also states "Spells cast from tablets do not have Penetration bonuses unless they are built into the spell’s level by the author". I am not sure I understand what this means. One way to read it is this. If I want a Penetration 10 tablet for a Level 20 spell that I have mastered, I create a tablet for what's effectively a Level 20+10=30 spell. When someone casts it from the tablet, it automatically has Penetration 10 regardless of the casting score achieved, as long as it's cast successfully. Is that right?

Casting tablets are brief but highly detailed instructions, so they probably take up only a few pages (a scroll would easily hold a casting tablet). Presumably the instructions must be very precise and clear, so they must be drawn with extreme care and that's why they take as long as lab texts to make (which are collections of notes that even when clearly written take a season to fully decipher and understand).

R/D/T: are fixed by category; this prevents people from using Flexible Formulaic Magic or Boosted Magic to vary them. Type of AC is based on the author, and I presume it means something like "Use a lock of hair" or "A cup of water from the lake" or the like - mostly because magi can fix ACs to last forever, so the duration of the AC isn't a factor.

Penetration bonus would add directly to the spell's level, which is the target for casting the spell. It makes the tablet harder to cast.

It might be worth noting that a Casting Tablet can only be made by someone who has mastered the spell. The economics of lab text duplication and copying imply that casting tablets will be much more scarce. There's far fewer people able to write them. Magi with Flawless Caster make great producers of Casting Tablets, and there might even be a small network of such people who produce the great majority of casting tablets in use.

Well, what kinds of things would a tablet be used for?

I can think of two major uses. One is a Wizard's Communion tablet, and those are probably the kind of thing you can get copied for a pawn - they're the kind of thing you use to turn apprentices into communion slaves. The other is a Big Ritual tablet, which you use because it's easier to follow directions than to learn a spell that powerful from a text and then cast it yourself, and that wouldn't require Flawless - a lot of magi who have Big Rituals master them to reduce the botch dice.

Are casting tablets even in the 5th edition? I know they are mentioned in Covenants but not in the main rule book.

They're in 5th edition - as you said, in Covenants. They're not in the core rules because they're not really typical casting.

So much about Casting Tablets really doesn't make sense.

Early editions of Ars Magica allowed the casting of spells from "normal" texts at a penalty. Whether or not this was necessary or beneficial to the game, at least it felt true to stories about wizards.

The current version, with optimized casting texts and the implication that there's a cottage industry of magi making and copying out these things just doesn't feel right at all to me. It's an awkward and unnecessary halfway step between spellbooks and actual spell learning.

More to the point (in my opinion) it allows for discount enchanted items.

Agreed. On all counts.

We tend to ignore their existance.

I don't recall having seen them in an Ars Magica product since the Covenants rules came out. I could be wrong of course.

I remember a casting tablet in LoH. Ser the maga who worked with realms.

Various casting tablets appear in THROUGH THE AEGIS, which is of course where they would appear.