Auda spends most of her time sitting in bed staring at the wall but doesn't seem discontent about this exactly.

He does eventually ask, "Are you bored?"

"Hmm?"

"Would you prefer to have something to do? I don't know what if anything you do for fun but if I were sitting around not doing anything I'd be bored."

"I used to sew things? One of the fairies tried to have me copy written things but I wasn't very good at it."

"Do you like sewing? Do you want, like, embroidery stuff or anything?"

"It probably won't be very good but it'd be nice to try."

Cam does not know a ton about embroidery but he can guess at some nice even threadcount muslin and a lot of embroidery floss colors and a thimble and - "I do not seem able to do needles or scissors, possibly because they are sharp, lemme trade a faery for those, I bet they have them." Light.

Same fairy! They do in fact have those.

Cam offers the nice china plate in exchange and presents Auda with the needles and scissors.

Then she will sit there embroidering instead of sitting there not doing anything!

Oh good!

He decides it is safe to check his mail, but he doesn't have any, probably because he's been here for, like, minutes, even if this is a parallel reality. That really makes it hard to check up on anything.

He looks up a mechanical watch that counts milliseconds and can't find one. He settles for a normal mechanical clock and makes one of those.

It works fine, just, like, slowly.

Cam decides it will not cause any time paradoxes if he reads a novel. He makes one.

Then his afternoon will pass peacefully and uninterrupted.

He and Auda have spaghetti and meatballs for dinner, and when he finishes his novel he goes back to the faery science books.

The faeries are batting above the average for tenth century humans but confused about many things! They're not sure if the stars move and whether planets and stars are distinct things. They seem unclear on the existence of air as a phenomenon distinct from vacuum. They suspect the world of being round but not confidently.

Gosh. Maybe next time he sees Science Brother he will issue corrections.

A different brother actually stops by first! "I heard you have thoughts about monetary systems!" he says by way of introduction.

"I have information from a more advanced civilization about them, does that count? I got what seemed like a pretty abbreviated summary from your brother about how it has been discovered to interact with debt stuff."

"Yes, that counts! Tell me about it."

"The humans I'm accustomed to use money on a massive scale! They don't do it for minor personal favors within close relationships or to negotiate basic public-space type etiquette, but they use money to buy basically all other kinds of goods and services that aren't considered 'too cheap to meter' - such that figuring out how much to charge a given consumer costs more than the amount of good or service they'll realistically consume. There are several different kinds of currency and used to be more, which had fluctuating exchange rates depending on the prosperity and stability of the populations that used them. It was originally popular to use physical tokens of exchange, at first things that were valuable in themselves - standard sizes and shapes of metal, usually - later with easier-to-manipulate paper placeholders theoretically redeemable for such things, later they dispensed with the theoretical redeemability, later it became more convenient to represent amounts in pure abstraction without a physical correlate and then that became almost universal because demons are really good at forgery of physical correlates."

"Huh! How do you represent amounts in an entirely non-physical way -"

"We have machines," he waves his computer, "that are good at manipulating data, and it's possible to store the data in such a way that it's hard to mess with it if you are not an entity authorized to do so, so you store 'so and so has this many dollars' and then only the agencies entrusted with making transactions on so-and-so's behalf can adjust that number."

"Huh! It seems like you could get all of the good things about debt that way but have it entirely tuned to what people actually want."