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# How to use Ocular & Stage Micrometer for Calibration

 I want to measure the sample size under the microscope, 　　　Should I use Ocular Micrometer？ 　　　　or Should I use Stage Micrometer？
To put it simply
 ● An ocular micrometer is used for measuring the size of objects ● The stage micrometer is used for calibrating the ocular micrometer. (for more accurate measurement)

 ■　How to Use an Ocular Micrometer

 When an ocular micrometer is set correctly inside the eyepiece, it should enable to see a sample and an micrometer scale simultaneously when you look through a microscope. By determining single pitch length of an micrometer scale, you will be able to measure the actual sample size. ** Under the microscope, the single pitch length of an micrometer changes as magnification of objective lens is changed. Formula is : Pitch Length of Ocular Micrometer (under the microscope)　= [Actual Micrometer Pitch Length］　÷　［Objective Lens Magnification］

 Example :
 ● Below explains the measurement of a glomeruli (of the kidney) with following two premises. 1. Ocular micrometer model XY11 is used. XY11 has 0.1mm pitch (100μm) 2. Objective lens has a 20x magnification. ● Applying these numbers to above formula, one pitch of ocular micrometer in this scenario should be equal to 5.0μm (= 100μm ÷ 20). Since the glomeruli spans 23 pitches on the horizontal scale and 22 pitches on the vertical scale on micrometer, it measures 115μm (5μm x 23) by 110μm (5μm x 22).

 Obj Lens Mag Magnified Pitch Length 10mm /100 divisions / pitch 0.1mm is used 5 x 20μm (= 100μm ÷ 5) 10 x 10μm (= 100μm ÷ 10) 20 x 5μm (= 100μm ÷20) 40 x 2.5μm (= 100μm ÷ 40） 50 x 2μm (= 100μm ÷ 50) 100 x 1μm (= 100μm ÷ 100)

 ● First, position stage and ocular micrometer in a way both scale are lined up complete parallel (to derive correct and accurate magnification from error margin) ● Below illustrate stage micrometer NOB1 (1mm/100 divisions = 10μm pitch) and an ocular micrometer S11 (10mm/100 divisions = 100μm pitch). objective lens magnification is at 20x. ● If magnification rate is correct, 10 pitches of stage micrometer should be equal to 20 pitches (2000μm) of an ocular micrometer (=[1 pitch of ocular micrometer is 10μm] x 10 pitches x [Objective lens x20] )Instead, in below diagram, 10 pitches of stage micrometer shows equals to 21 divisions of ocular micrometer,therefore it can be calculated that magnification of objective lens is x21. ● To achieve the calibrated measurement of the sample, multiply the measured value of the sample by the labeled magnification of the objective lens divided by the actual magnification ratio. (Ex. Calibrated measurement of sample = measurement of sample × labeled magnification ratio ÷ actual magnification ratio) (Calibration ratio = 20/21 = 0.95)

 How to Install Ocular Micrometer An ocular micrometer is a glass disk with ruled scale on the surface which is etched in chromium. Please insert it into the eyepiece with written surface facing to objective lens (downward on below image)

■ How to identify front and reverse side of ocular micrometer.
Micrometer (scale and numbers) is printed on the glass with chrome.
When printed side is identified, insert ocular micrometer to eyepiece fixing bracket
with printed side facing downward (toward objective lens - refer also to above installing instruction)
Here explains how to identify front (printed side) and reverse side.

 1. Shed light on the micrometer and let it reflects in a way that printed numbers and scale will be turned silver.

 Unable to identify sides without the reflection of light.
** To generate enough reflection, large area lighting is recommended
** Eyepieces lens can be used as loupe and it helps you for installation

 2. When there is no shade, it is reverse side

 2. When there is shade, it is fron side (printed side)