Sentence:  Drawings and pictures are more than mere ornaments in scientific discourse. Blackboard sketches, geological maps, diagrams of molecular structure, astronomical photographs, MRI images, the many varieties of statistical charts and graphs: These pictorial <WSD>devices</WSD> are indispensable tools for presenting evidence, for explaining a theory, for telling a story. 
Meaning of the word marked with <WSD> tags:  A project or scheme, often designed to deceive; a stratagem; an artifice.