The Hydrion Insta-Chek pH Pencil is used to measure the pH of any surface or solid. It measures from pH 0-13 in full pH unit increments. No technical training is necessary. To measure the surface pH just wet the surface with distilled water. Stroke the surface with the pencil. Wait approximately 30 seconds and compare the resulting color change with the color chart. The pH Pencil is used to detect acid or alkali residues and may be used to measure the pH of any of the following: Paper, Lumber, Concrete, Cement, Plasterboard, Pre-painted surfaces, Painted Surfaces, Textiles, Skins or Ceramics. Micro Essential Labs #: P-12M.