Why should you always start with low power when using a microscope?
You don't have to its just to see the different cycles.
The higher the power, the more difficult it is to have the item being viewed centered in the viewing field. However at lower power the viewing angle is wider and it is easier to find and position the item in the field. So we start by centering the item in the field at lower power, increase the power and center it again.
I'm not sure if I understand the question. When using a compound microscope, you always want to start by adjusting the coarse adjustment under low power (like 4x) until you have whatever you are looking at in focus. Then, without moving the adjustment, go to the next power (like 10x or something) and use the coarse adjustment only a little and then use the fine adjustment to get it into focus again. Without touching anything…