This is the collimator, present table, telescope, this is the present. This is the base of the present, this is the rough surface, square in shape. The base of the present is placed towards the telescope in short base towards the collimator. Now the lamp is sodium vapor lamp and we are going to find the wavelength refractive index of the material of the present. Initially the radium screw under the telescope is open, the telescope is now moved towards the corner of the base. Now, moving through the eyepiece, moving through the eyepiece, the image of the eyepiece. This is how the slit appears, when it is used to go to the one side of the base, one side of the base. Now, it is focused sharply by using this screw. This focused very sharply, the image is sharply focused using this screw. Now, the radial screw is tight and closed. Now, using the tangential screw, that is the fine adjustment screw, the position of the slit can be adjusted towards the vertical cross layer of the telescope. This is how it is adjusted. Now, the slit is coinciding with the vertical cross layer. There will be two wires there, one with the vertical cross layer and another will be the horizontal wire. Now, the slit is coinciding with the vertical cross layer. Now, the radial is noted in the vernier one. Vernier one has vernier scale in which the ratings are from 0 to 30 and find the 0 here, this is where the 0 is. Using a hand lens, a convex lens you can see the position clearly. Now, the rating which is coinciding with the 0 of the vernier here at the bottom, that is the main scale. The rating that coincides with the 0 of this vernier will be taken as the main scale for the vernier coincidences. The vernier coincidences with the reading on the vernier scale, which exactly coincides with the main scale. The reading on the vernier scale, which exactly coincides with the main scale, is the 0 and 30 always. Now, this is vernier one period. Similar procedure is done for the vernier 2. So, here again the same procedure is done, another vernier scale is here. So, whichever reading on the main scale, which coincides with the 0 is taken as M. Z. And whichever reading out of the 30, which exactly coincides with the any of the main scale, you take another vernier one. So, the two readings are noted down, this is the position or 1. Now, to do the R2 position, incidentally the radial screw is open and the telescope is open. And then it comes, parallel to, which are there.