Topic: Alchemy: how would you make...

[MisterK]

... a pair of books, where if something is written in one, the exact same thing is instantly written in the other [regardless of distance] ?

or any pair of devices where one records something (e.g. sound) and the other reproduces it.

[jdale]

Symmetrical Linkage on the Psychographer list Personal Empowerment. 9th level spell, unlimited range. RMU.

Alternatively, you could treat it as a communication where the specific design (i.e. pair of books) is just the form the magic happens to take. Then you could either have a Daily or Constant effect with whatever communication spell, with whatever range and usage limitations it might have.

[MisterK]

Oh, great !

Instant, wireless, unlimited range point to point communication as a fairly low-level enchantment. State rulers, criminal cartels and conspirationists alike around the (fictional) world thank the RMU designers greatly :p

[jdale]

It's limited in the kind of information you can send, basically like writing email without the ability to include attachments. But useful.

Creation would take 16 days (9 for Symmetrical Linkage, 7 for Work Organic for paper), with a market cost of 176sp. Not going to become ubiquitous like smartphones but not out of reach for a successful merchant.