Function dev

Mean absolute deviation from the average. Valid scalar defaults accumulate deviations oldest first and omit nonfinite results. Supplied skip uses period finite observations and holds across gaps; propagate requires a full chronological window. Ties retain their multiplicity and warmup is NaN. Invalid option-path periods throw RangeError, malformed options TypeError. Periods must be positive safe integers.

Bar-aligned lengths select the current deviation window; NaN lengths give gaps.