*Independent variable* is a quantity that is not dependent on another quantity, which is either (a) a quantity chosen before an experiment or race, or (b) an ever-increasing quantity. *Dependent variable* is a quantity that whose value is a function of another variable.

*Length* is measured by a rigid rod. *3D length space* is length measured in three directions of motion.

*Duration* is measured by a stopwatch, timer, or clock. *3D duration* is duration measured in three directions of motion.

*Length space* is (1) 3D differentiable manifold of length; (2) the order of events on a stance line; (3) *the stance*, the reading on an arcloge.

*Duration space* is (1) a 3D differentiable manifold of duration; (2) the order of events on a time line; (3) *the time*, the reading on a clock.

*Length-duration* is the 6D manifold formed from 3D length space and 3D duration space. *Worldline* is the path in length-duration traced out by an object in motion.

*Displacement* is the vector between two points (events) on a worldline. *Distance* is the magnitude of a displacement.

*Dischronment* is the vector between two points (events) on a worldline. *Distime* is the magnitude of a dischronment.

*Reference frame* (or frame) is an abstract coordinate system and set of reference points in 3D length space that uniquely fix the coordinate system and standardize measurements. *Rest frame* of a body is the reference frame in which the body is moving at zero speed, which is the time conversion pace.

*Reference timeframe* (or timeframe) is an abstract coordinate system and set of reference points in 3D duration space that uniquely fix the coordinate system and standardize measurements. *Freeflow frame* of a body is the reference timeframe in which the body is moving at zero pace, which is the stance conversion speed.

*Proper length* is the length of a body measured by a rigid rod moving with it. *Proper time* is the time of a body measured by a clock moving with it.

*Lorentz transformation* is a set of equations that relate length space and duration space coordinates of reference frames moving at a constant velocity relative to each other.

*Dual Lorentz transformation* is a set of equations that relate length space and duration space coordinates of reference timeframes moving at a constant legerity relative to each other.