System Dynamics
Stock
An amount accumulated at a point in time. Here it is the number of accepted repairs not yet finished.
Close equivalent — in this context
Level
Within System Dynamics
Both name the accumulated quantity here.
Related — not interchangeable
Inventory
Inventory in an operations context
Inventory can be modeled as a stock. Count bikes or parts consistently; neither is automatically the unfinished-job queue.
Different — watch the distinction
Repair capacity
Repair capacity measured in jobs/day
Potential daily throughput is not the number of jobs waiting. This is our application of the units; a stock of mechanics would have units of people.
This comparison is an editorial synthesis for this example. Other contexts can use these words differently. Cybernetics, Critical Systems, Complexity and Network comparisons are not yet reviewed here.
See it at the bike shopWhere this comes from
- Introduction to Project Dynamics · slides 28–30
James Lyneis · MIT OpenCourseWare · 2012. Stock/level and flow/rate distinctions.
The bike-shop case and numerical model are original illustrative exercises from Renaissance Solutions. These institutions have not endorsed this exercise.
All sources and credits