I’ve lost count of how many times I’ve had to look down the microscope as a PhD student, and I only ever had to look down the microscope for one reason and that was to check for cell confluency. This was a critical step during in vitro cell work. It was the time a crucial decision needed to be made as to whether the cells growing in the flask were confluent enough so the cells could be split or seeded? Or if the cells were not confluent and needed to be left to grow for another day or two?