Readers may or may not know the details of a lab report. You shouldn't assume that they know a test well enough to fill in the report's blanks or that they know anything about the actual lab. Check with your instructor to know who your audience is. To help you describe your lab thoroughly, assume you're writing for a peer in your class, a student who knows what the instruments are, but who doesn't know any of the details of what you're doing. Or, assume you're writing for engineers who will use your information on a project. They may not be familiar with all the terms, so you should explain the lab to them.