 Hello friends. Let me introduce myself first. Myself Mishriya S. K. Kulkarni, Assistant Professor, Department of Civil Engineering, Balchan Institute of Technology, Sholapur. Topic of our today's discussion is Method of Finding Missing Entries in a Page of a Level Book, by Collimation Plane Method. Learning outcome of today's session. At the end of this session, students will be able to evaluate missing entries in a level book page by Collimation Plane Method. Introduction. Friends, what happens? Sometimes some entries in a level book page may not be visible or may not be readable clearly and one will have to compute them from the other available readings. Therefore, this is necessary that one must know how to find in such cases the missing entries in a level book page. We will go for one exercise which will make the things more clear. Here, one level book page is given in which some entries are missing and we are asked to find out the missing readings and calculate the reduced levels of all the points which are there. Here, stations are given, backside reading. X1, this is missing one. Then intermediate sites are there. Four-side readings are the Collimation Plane RL. RLs of stations and remarks. First reading is always on benchmark, we know. Its RL is known 105.00. But Collimation Plane RL, this value, X4 is missing. It is not given. So, in such cases, what we can do? We can find such an alternative which will give us the reading which is unknown in a fastest way. For example, in referring to these two readings, intermediate site 1.660 of station number 3 and RL of this station is also given. So, from these two readings, we can find Collimation Plane RL easily. So, we can first find out X4. Once we get X4, we can find X1 easily. Likewise, we have to decide which one to find first. So, here we will do the calculations like this. We know these relations. Collimation Plane RL is equal to RL of benchmark plus backside reading. This is, let it be equation 1. And RL of any point is equal to Collimation Plane RL minus level reading at that point. This is also known to us. Let this be equation 2. So, using this second equation, we can find now Collimation Plane RL X4. So, we know Collimation Plane RL X4 minus 1.660 must be equal to 104.250. So, only one unknown X4 is equal to 105.850. So, enter the value here X4 is 105.850. Once we have got X4, now X1 can be found easily. Because RL of benchmark is there, Collimation Plane RL is there. So, backside reading can be found from which equation? Equation number 1, Collimation Plane RL is equal to RL of benchmark plus backside reading. So, putting the values in this equation, what we get 105.850 is equal to 105 plus X1. X1 is 0.850. One can easily find this value also. So, backside reading is available. Now, these two readings we have found, which next we can find? We are having here X4. We are having intermediate side reading. Collimation Plane RL, intermediate side reading. We can find X6 easily from the relation equation number 1. Collimation Plane RL minus IS reading here, intermediate side reading must be equal to RL of this station. So, using again the equation second. So, what we get? X6 is equal to 104.250. This is the value. Once we have got this, let us see now which next value we can find. Now, here we will see that we will observe that change point is there. How to know which is the change point? See here, foreside reading and backside reading both are written in the same row. This indicates that this is a change point. So, X8 means in the remarks column here, there should be change point. Remark should be there. So, Cp is required to be written here in this fashion. So, record it. So, now, once we know that this is change point, how to find collimation Plane RL, new collimation Plane RL, because instrument position is changed now. For that, we need to know the backside reading here. Or here you are having intermediate side reading at station number 5 and here RL of that station is known. From these two readings, we can easily find out collimation Plane RL by using equation 2. So, X5 minus 1.250 is equal to 103.050. This will give us value of X5. So, how much is X5? X5 is 104.30. So, enter it here, X5, collimation Plane RL. Once you have got new collimation Plane RL, so, finding X2, which is unknown missing. So, again it is easy one. RL of station plus backside reading gives us collimation Plane RL. So, here this X2 only will be unknown and we will get that value also X2 is 0.900. Calculations are shown here. So, X2 is also obtained. Now, what remains? Next unknown value is X7. So, here we know collimation Plane RL, we know reading intermediate side reading of station 6. So, X5 minus 1.855 will be equal to RL of that particular station, station number 6, that is X7. So, X7 is also found it is 102.445 down here. Now, which is the next unknown value, unknown value is X3 now, 4 side reading, the last reading, right. And we know the RL of that last station, station number 7, we know the collimation Plane RL. One can easily find this particular value also. So, collimation Plane RL minus X3 is equal to 101.315. So, this is collimation Plane RL minus X3 is equal to RL of that station. So, X3 is 2.985, right down here X3 2.985. So, we have found in such a fashion all the unknown values. So, finding missing entries is not at all difficult. One should know the procedure one he or she can easily find it out. The backside readings their summation is taken check whether this summation given matches or not. Then four side reading its summation is also given we can check it. And then last RL minus first RL this particular arithmetic check must get satisfied. Sigma backside minus sigma four side is equal to last RL minus first RL. So, check whether this arithmetic check is obtained or not. These are the calculations. Now, friends let us pause a little here. There are two questions for you. First question is why missing entries problem arises? And second is how arithmetic check is taken? You know the answers of these two questions. Write them neatly on a piece of paper. We will pause a while here. That's good. Now, what are the answers? Why missing entry problem arises? Because there may be some readings. There might be some readings which are not readable or not clear. So, in a label page book. So, what you will have to do? You will have to find those readings from other available readings. So, we must understand how to solve such problems and this problem is there. Now, how arithmetic check is taken? Arithmetic check is taken by using the equation sigma backside minus sigma four side is equal to last RL minus first RL. This is the arithmetic check in collimation plane method. Now, summation of backside minus summation of four side. It comes to be minus 3.685 and last RL minus first RL also comes to be minus 3.685. So, the equation is satisfied. Our check is obtained. There is no need of revision of calculations. We know arithmetic check gives us idea about only correctness of calculations in the table. It does not give any idea about correctness of readings remember. So, we must take the arithmetic check at the end of our calculations and then only the work will be complete. These are the references for today's session. Go through these. Thank you.