invariable

The speed of light is an invariable constant in the vacuum of space.

(Chinese) 光速在真空环境下是一个恒定不变的常数。

Unlike the fluctuating weather, her invariable routine began with a cup of black coffee at 6 AM.

(Chinese) 不同于多变的天气，她那不变的日常总是从早上六点的一杯黑咖啡开始。