When you reference worksheets from within a parent worksheet, PTC Mathcad can optionally cache the referenced worksheet content. This enables you to use and calculate the parent worksheet even when the referenced worksheets are not accessible.

Worksheet caching is enabled by default, but you can control this setting on the Input/Output tab.

With caching enabled, when you save and close the parent worksheet, PTC Mathcad stores those regions from the referenced worksheets that are relevant for the calculation. When you reopen such a saved worksheet, if any referenced worksheet is unavailable, PTC Mathcad uses the cached content for calculation. In this case a warning appears on the include region stating that the referenced worksheet is not accessible.