These are several things that create value for the money:
- Durability
It should be made with materials that could sustain themselves for a long period of time.
- Identifiability
Money should be easily recognized by the people who use it
- Portable
Money should be in a size and shape that are easy to be carried around by people.
- Usefulness
Money should have trading powers that people could use to obtain another goods or services.
The invention from the song dynasty that improved clocks was: The clock tower/clepsydra clock
This invention is the first type of clock that utilized the <em>escapement mechanism </em> that is applied by many European countries around 2 centuries later to produce their clocks.
I think the answer is rivers.
