The book is written out of personal conviction learned through patient-care delivery while interpreting arterial blood gas (ABG) reports. There are difficulties and odds experienced in understanding these interpreting reports, which are to be avoided. Hence, there was a quest for simplification of acid–base analysis for everyone, including beginners, undergraduates, postgraduates, and physicians, in every discipline of medical science. The school-based simple mathematics and chemistry are revisited and applied at every step of documentation for an inductive logic to a correct diagnosis in clinical situations. The elements, oxygen (O2), hydrogen (H2), and carbon (C), are found in every organic matter in various combinations. As per Lavoisier, hydrogen (from Greek hydro meaning “water” and -gen meaning “generator, begetter, or maker”) and oxygen (from Greek oxy meaning “acid producing” and gen meaning “generator”) react with various elements to produce various products. The simplest one is water (H2O). A substance or molecule that contains O2 has acidic properties, more often in organic matters. The element O2 plays a major role in many of the most important naturally occurring chemical reactions. Digestion is a natural chemical process with many reactions producing acids and alkalis. Its measurement is aptly done by pH estimation. The scope and range of the book are evident from the table of the contents, which are visible throughout with a basic approach. The whole treatise here is on O2 and H2 with their reactive derivatives carbon dioxide (CO2) and carbonates, with life processes being active and intact. It is not a comprehensive book but rather a guide which will help every reader to solve problems fast at first hand.