The Rest of All Possible Worlds: Pocket Items

There are all sorts of interesting devices these days. Bigger and better telescopes, dense almanacs, precisely fitted sextants. And since then there has been a market for portable versions of these. 

Bluntly, these are toys for rich men.  Few need a sextant at any moment, let alone a smaller, fiddlier, uncomfortable, easily broken version. But one or two people have found these very useful indeed - and not just as portable trade pieces.

Here's a few - others may exist.

1. Within a stubby silver cylinder ticks A Perpetual Calendar. Turn shells of year and system on the outside to the indicted marks. Good for all Calliste, valiant attempts to indicate assorted high days and holidays of the Alamgir Empire and the Bronzemount Free State.
2. The slim brass case of a Tally-Box. This can add, subtract and convert the Pavaisse Mark, the Pavaisse Trade-Weight and the Malmeric Gold Piece.
3. Extending from a smooth horn box is a Microscope. The base of the box turns into a mount for whatever minuscule thing you wish to examine.  
4. A carved wooden case reveals a series of ivory Rabdological Rods.
5. A brass-half moon unfolds into a small Astrolabe.
6. Set in velvet, a fine golden set of Scales and a set of tiny weights.
7. A Mage's Chronometer. Perfectly mundane in construction, but allows the user to set a series of markers for when they can re-apply themselves to a spell.
8. Folding wood and gilt Sundial (sun not included).
9. Set in a rotating gimbal in a little pale box is a Mundane Lodestone. This points to the least magical place in a Ninety-Nine Mile radius of the user and is often used by insufferable wags at parties. 
10. Some men hold the world in their hands; you hold it in your pocket. Or at any rate, an ornate and definitely accurate Globe.

As for some actual rules:

The value of any of these in working order is meaningful - at least a month's wages, say. It may be difficult to find someone who will buy it, however. 

None of the above meaningfully contribute to encumbrance. 

This is not an age of mass production. At most, there are a dozen items of this kind coming from the same artificer's studio. Finding an exact replacement outside the maker's home city and years after it was made will be difficult.

Spare parts are non-existent. You will need to find someone who can work from scratch.

It may be that whoever made the device in the first place lacked certain details - the knowledge of annual holidays in Transmontane Tsymric may be patchy in High Malmery.

There may be lands where all of the above is untrue! 

If you are ever in Cambridge, consider visiting the Whipple Museum.