Have you found a genuine free source for Edition 16? Share the link in the comments (only if it’s legal!) or tell us which chapter you’re stuck on.
One of the standout features of the K.C. Sinha Calculus book is the structured hierarchy of problems. The book does not throw the student into the deep end immediately. It begins with:
Skip the "Objective Questions" at the back of the chapter until you finish the book. Do the solved examples first. Cover the solution with your hand. Try for 5 minutes. Then look.
Go get the book. Open to Chapter 5 (Differentiability). Solve 10 problems. Come back and thank me later.
Is the "BEST"? For mastering the mechanics of calculus for Indian competitive exams? Absolutely.