# Point entities & Interval entities (Bookkeeping)

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From my studies as an electrical engineer, I remember that there are interesting correspondences between certain physical environments. E.g.: There is a certain correspondence between certain mechanical systems (mass-damper systems?) and basic electrical circuits. These analogies are actually the basis of analog computers: You can simulate mechanical systems by applying these electrical analogons.

If I remember correctly, a key observation was to distinguish between point entities and interval entities. An example of a point entity is electrical current, or the current of water flowing through a river. An example of an interval entity is electrical voltage or elevation change between two point of a river.

In bookkeeping, there also seem to be point entities and interval entities:

• Point entities: Balance sheet & related accounts (rekeningen)
• Interval entities: P&L account & related accounts (rekeningen).

There are ways to convert an point entity into an interval entity. An example is the Profit Equation, that takes a balance sheet-related entity (equity) at two different moments in time, and calculates the difference between them.

Maybe bookkeeping is another example of the aforementioned analagy between certain physical systems?

Or a step further: The difference between an entity and the change of that entity (like over time, or over distance, etc.), points to differential equations. And maybe that's not too farfetched. E.g., the dialectics of progression (wet van de remmende voorsprong) seems a bit similar to the differential equation for calculating the terminal speed of a raindrop.