unvarying

adj

1. Persistent, constant, changeless.

   “You can be sure of our unvarying attention.”

   “In the United States, where the railways are 90 per cent. dieselised today, diesel-electric power is the unvarying rule for independent locomotive units, and the only motive power exceptions are the highly successful 600-h.p. diesel-hydraulic railcars of the Budd "RDC" type, of which between 300 and 400 are now at work.”

2. Lacking variety; having a uniform character.

   “The prizewinning carrots were of an unvarying size.”