So I have been going through a book on physics-based mathematics. I have seen the author using natural units (h = c = 1) in formulae. Why is this done? Most importantly, doesn't it mess up the true calculation? For example, take e = mc^2. If I set c = 1, it becomes e = m. So if I am given a mass and have been told to calculate the energy, it's the same as the given mass! How is this all consistent? I don't get the concept. I would be glad if someone would explain it in a simple manner. Thanks in advance!