 So, now the last thing that we have to consider, this is not a variation, this is not a parameter, this is an outcome, so very lifting gas volume. Now the thing is that we know that this envelope, LTA gas envelope, it continuously leaks gas. Now, what is the typical leak rate of gas from an envelope? Yeah, 1 liter per meter square per day, yes, 1 liter per meter square per day, that is one of the benchmark values, people try to beat this value but if it is worse than this, you think that the envelope is not a very good envelope, correct. So over a period of time, gas is going to leak from the envelope, a time will come when the lift, gross lift will not be able to overcome your requirement, so you may have to pump in more gas. During that case, the weight, the volume of the lifting gas and also the weight will change and when you pump in the lifting gas, the total volume of the lift is the same. So, airship operators are regularly top of the envelope. The frequency varies, some people do it on a monthly basis, some people do it on a three monthly basis depending on at what is the leak rate that they are getting. So, the moment you top of the envelope, the inflation fraction will increase because there will be more gas, the volume occupied by the gas will be more compared to the total volume and if you do that, the net static lift also will be changing, increasing. So, if you assume y equal to 1, that means the whole envelope is full of pure gas and if you ignore TSH, also there is no super pressure, I am just knocking off these terms for simplicity. Then the net lift is equal to 1 minus I d pure gas into P s I k b by T A. So, delta n because of delta V lg will be essentially a subtraction and subtraction is already taken care, so if you replace V with delta V, but delta V lg not envelope, envelope delta n remains the same. So, if you add delta V lg amount of gas, then the additional net lift will be 1 minus R d P g into P s by T A into I into k into delta V lg, there is no I here because you are not looking at a fraction of the total. So, if you are adding so much gas, you will directly get so much of additional net lift. Now, how can we bring in simplification here? So, the volume of the lifting gas is nothing but the pressure of the lifting gas under standard conditions divided by the pressure at ISA condition into temperature upon TSP into we should do that. So, this is basically equating conditions which are standard and ISA. So, therefore, the additional net lift will also be expressible in terms of P STP and T STP if you use V lg STP. So, therefore, the change in the volume that you need is directly proportional to how much lift you are going to generate delta n is a required lift. If you want some required lift that into TSP upon P SP into 1 minus R d P g into k is what you have to add. So, if for instance you realize that we have to take care of loss of lifting gas by putting so much to generate so much lift, this is a simple way to estimate how much gas you will have to put. And when you put more gas then the change in the inflation fraction will be the delta V lifting gas added upon the envelope volume.