What focus adjustment should you use to focus on the specimen under the high power?

When focusing on a specimen under high power, you should use the fine adjustment knob. The coarse adjustment knob is typically used only under low power to prevent damage to the slide or objective lens. The fine adjustment allows for precise focusing, which is crucial at high magnifications to achieve a clear and sharp image of the specimen. Always ensure that you start with the lowest power objective before switching to high power for safety.