Units

Warning: Wiki should not be edited directly. Edit the files in the ./wiki/ folder instead and make a PR.

These are notes around the topic of units that need to be reorganized.

• Wikipedia's page on System of Measurement points out that there are 'monetary units' as well
• The Wikipedia page on Unit of Measurement define is as a definite magnitude of a quantity. The important part here is that the SI system is specialized to physical quantities of a particular kind, and doesn't cover all quantities.
• Some entertainment can be derived from reading the List of Unusual Units Measurement. Here too are some units related to things that aren't expressible in SI. (That page links to even weirder stuff as well).
• Relatedly to units is the concept of Level of Measurement. This is a far-future item for Drasil to 'learn'.
• There's a standardized way to encode units of measure. It includes radian. There is a really nice list of units on that page as well - something that might be good to teach Drasil "once and for all".
• We have struggled with a broader "classification system". The page on Quantity is a good place to get an idea of the complexity.
• There is however an International System of Quantities ! (See below for why this is important). There ISO/IEC 80000 that covers this.
• There are rules for writing SI units on the SI page

The SI page contains the following extremely important paragraph:

On the other hand, several different quantities may share the same coherent SI unit. For example, the joule per kelvin (symbol J/K) is the coherent SI unit for two distinct quantities: heat capacity and entropy; another example is the ampere, which is the coherent SI unit for both electric current and magnetomotive force. This is why it is important not to use the unit alone to specify the quantity

Another example is the units of work (N m) and the units of torque (N m). Both work and torque have the same fundamental units, but torque is a vector quantity, while work is a scalar.

There is an accompanying footnote also of interest

As the SI Brochure states,[1]: 140  this applies not only to technical texts, but also, for example, to measuring instruments (i.e. the instrument read-out needs to indicate both the unit and the quantity measured).

---

Here are some relevant papers:

• Digital Representation of Scales and Units for Temperature and Related Quantities The principal point here is 'scale', but it also introduces a so-called "M-layer" which is more about quantities themselves.
• Digitalisation of units and dimensions is another paper that makes the point that quantity classification goes beyond just units.