Why should the fine adjustment knob be use only with the hpo in microscope?

The fine adjustment knob should only be used with the high-power objective (HPO) in a microscope to achieve precise focusing without risking damage to the slide or the objective lens. Using coarse adjustment at high magnification can lead to the lens crashing into the slide, potentially breaking the slide or the lens. The fine adjustment allows for delicate, minor adjustments needed for sharp focus at high magnification. This ensures optimal clarity and detail while maintaining safety for the specimen.