Why should the microscope be calibrated for each objectiveand prior to each use?

The microscope should be calibrated for each objective and prior to each use to ensure accurate measurements and observations. Different objectives may have varying magnifications and optical characteristics, which can affect the scale of the images viewed. Calibration helps to align the measurements with the actual dimensions of the specimens being examined, minimizing errors. Regular calibration also accounts for any potential drift or changes in the microscope's performance over time, ensuring consistent results.