Einingarreglan

Einingarreglan is a guideline used in mathematics, physics, chemistry, and engineering to manage units in calculations. It emphasizes that numerical values are meaningful only together with their units, and that calculations must respect how units combine and convert. The rule is commonly taught in Icelandic schools and appears in science curricula as a practical tool for ensuring accuracy and interpretability of results.

Core principles: In addition and subtraction, quantities must have the same unit; different units must be converted before combining. In multiplication and division, units multiply or divide according to algebraic rules, producing compound units (for example, meters times seconds yields meter-seconds). When in doubt, one uses conversion factors and SI base units to keep track of dimensions. Dimensional analysis — checking that both sides of an equation have the same dimensional form — is a common application of the einingarreglan.

Impact and scope: The rule supports error prevention in laboratories, engineering calculations, and data interpretation. It also underpins unit conversion practice, enabling comparison and aggregation of measurements from different systems. While the exact formulation can vary between curricula and fields, the core idea remains: keep track of units as you compute, and only combine quantities that share or can be converted to compatible units.