Using a Graticule

Graticule - What are they? Some microscope eye pieces have small scale rulers built in to them. However, when you change the magnification, each division on the eye piece scale changes in value. Therefore it must be calibrated

How to Calibrate Another special ruler called a stage micrometer is used (it is put on the stage) This ruler is 1mm long and divided into 100 equal (equidistant) divisions Therefore 1mm = 1000μm so 1 division = 10 μm – this can then be used with each change of the objective lens to work out what each eye piece unit is worth

Example In this example it equals 15 epu. 1000 ÷ 15 = 66.6μm per eye piece unit You would then count the number of eye piece units that fill 1mm Example This is 1mm = 1000 μm

Eye piece magnification Objective lens magnification Total Magnification Value of 1 epu (μm) X10 X4 X40 25 X100 10 X400 2.5 X1000 1.0

Here is a cheek cell seen down a microscope using an objective lens x4. What is the actual length of the cell?

Here is the same cheek cell seen down a microscope using an objective lens x10 What is the actual length of the nucleus?