Some situations call for a fixed overhead of spare capacity (typically ports) which might be immediately available spare capacity in the event of card failure or to enable rapid provisioning for new customers.
This fixed overhead for a resource can be specified explicitly with the Minimum Slack Capacity input (MSC), found in the Capacity and Lifetime dialog:
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where there is no geographical Deployment to consider, STEM adds this MSC to any non-zero required demand before rounding up to determine how many units must be installed, thereby ensuring that there will always be the slack capacity required for as long as there is any current demand
- the MSC input is ignored if there is no current demand for a given resource
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the MSC input is not limited to the unit Capacity of a resource, so it can lead to multiple, wholly slack units being installed if so required.
For a resource with inputs Capacity = 50 and Minimum Slack Capacity = 15, the effect is just that the next unit will be installed when the demand exceeds 35, 85, 135, etc., rather than the usual 50, 100, 135 and so on.
See also 10.3.18.2 Minimum Slack Capacity and Deployment.