Accidental: Unforeseen event that alters the normal or expected course of things, especially one that causes damage to a person or thing.
ADJECTIVE. He had an accidental in the stands.
Assemble: To join various elements, especially pieces of wood, in such a way that they fit together perfectly, usually by making part of one fit into another.
VERB. He is assemble the puzzle together.
Calculate: Do the necessary mathematical operations to find out the result, value or measure of something in numerical expression.
VERB. He is calculating the operation.