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Find and click the Gizmos lab simulation that matches the name in your Canvas activity to launch the lab simulation (In this example, Gizmos: Chemical Changes).
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You may also use the Find Gizmos feature at the top of Gizmos by clicking in the search field and typing the name of the simulation that matches your Canvas assignment.
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Be sure to visit the Gizmos - Common Issues page if you run into any problems.