The pH scale is a measure of the concentration of acid or base a substance contains. By definition, the pH scale is the concentration of the hydrogen ion. The hydrogen ion is a characteristic of acids. High hydrogen ion amounts indicate high acid concentration, low hydrogen ion amounts indicates a basic concentration. The scale is graduated from 0-14. The numerically low end, 0-6.9, is the acid end. The closer the pH is to zero indicates a greater acid concentration. The mid point on the scale is 7; having equal amounts of acid and base making a neutral substance.