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Micrometry Linear measurement of cells Units of measurement in cell study • Millimeter (mm) – 1mm=0.001m • Micrometer (μm) – 1μm=0.001mm=0.000 001m • Nanometer (nm) – 1nm=0.001μm=0.000 000 001m The micrometer eyepiece How to use it • 1. Calibrate – Calibration slide (0.01mm) • 2. Set the microscope to low power and focus on the lines engraved on the surface of the calibration slide. • 3. count the number of lines – The total number of eyepiece lines (X) – The total number of calibration slide lines (Y) X=38 lines Y=10 lines note that the little lines mark off half spaces and that the first line is not counted because is shows the zero mark • 4. Calculate how much each line of the eyepiece measures. In step 3, 10/38x10μm=2.63μm • How big is this cell? 2.63μmx7=18.4μm • 5. under medium power • X=95 lines • Y=10 lines • 10/95x10μm=1.05μm How big are the cells? • 6. Do the same for the high power. (0.26μm) • 7. Now you can use the microscope to observe and measure things. Note that if you change microscopes, the calibration process must be done again for each of the objective lenses that you are using. Why? Because the magnification is different on different microscopes. To save time, only calibrate the eyepiece for the objective lenses that you will be using. More examples: • A tomato cell's nucleus seen at high power. How big is the nucleus? • An onion skin at high power. How big is a typical nucleus? • A banana cell at high power. How big are the starch grains?