Is it farther or further?
c.1400, from Old French rectifier, literally "to make straight" (14c.), from Late Latin rectificare "make right," from Latin rectus "straight" (see right (adj.1)) + root of facere "to make" (see factitious). Related: Rectified; rectifying.
rectify rec·ti·fy (rěk'tə-fī')v. rec·ti·fied, rec·ti·fy·ing, rec·ti·fies
To set right; correct.
To refine or purify, especially by distillation.