Stocks elements are elements which impart inertia and memory to a system. These kinds of elements are responsible for internally generating the dynamic behavior of a system. At any point in time in a simulation, the outputs of stock elements are computed based on the historical values of their inputs. Mathematically, stocks represent time integrals.
| Element | Default Symbol | Browser Icon | Function |
| Integrator |
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Integrates values. Also can compute moving average of a specified input. |
| Reservoir |
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Integrates (and conserves) flows of materials, allowing for upper and lower bounds to be specified. |
| Pool |
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More complex version of Reservoir, making it easier to model multiple inflows and outflows. |