(trigonometry) law of sines

(chemistry) A rule in chemistry that states that the sum of the hydrogen valence and the maximum oxygen valence is equal to eight.

(gematria, very rare in print) The rule according to which one digit may be added to or subtracted from the gematric value of a word.

An instrument consisting of a rule or frame, and a plumb line, by which the batter or slope of a wall is regulated in building.

(organic chemistry) A rule describing the outcome of certain addition reactions in organic chemistry.

An unspoken rule.

The ecogeographic principle that, within a broadly distributed taxonomic clade, populations and species of larger size are found in colder environments, and species of smaller size are found in warmer regions.

A rule that is understood to apply but does not exist in written form.

Ampère's circuital law

(rail transport) The steepest uphill gradient in one direction on a section of railway line, which determines the load that can be pulled by one locomotive over that section, according to the power rating of the locomotive. A typical ruling gradient could be 1:50 (2%). The ruling gradient can differ in the other direction on the same section.