How to calculate square root of a certain natural number without using calculator?

Well, this is my first post. I am a student currently studying at third year of my undergraduate course of mechanical engineering. In this post, I will share an interesting tip which is based on my own studies , experiences and observations.
The student nowadays are being too dependent on calculator and they need calculators even for the simple multiplication of 2*2. This post is not about those simple calculations.
So I am going to give some tips on how to find square root of natural numbers.
If you are asked
What is the square root of 36 you can easily say it is 6.
What is the square root of 49 you will reply 7.
But if you are asked square root of 40, then you will immediately start to search for your calculator.  If you are not the kind of student who need calculator for the multiplication of 2*2. Then you will say somewhere in between 6 and 7.
But if you want your answer precisely upto 1-2 decimal places then this trick will help you.
√40=6+(40-36)/(49-36) = 6.3
I think you have understood how this is done.
Let us look at another example
√60=7+(60-49)/(64-49)= 7.73
Now I feel you are clear
If you have already studied interpolation then you can see it is one of the application of linear interpolation.
However, you need to be good in division for solving this.
Practice is the solution to every mathematical problems.
If you do not practice it, then it will take a lot of time for you to solve it.
This is best in those scenarios when you need to find square root of certain number and you donot have calculator anywhere near you. This process is however lengthy. And I do not guarantee its accuracy for larger numbers
So, this was my first article. Please do comment your response after reading this.