per unit time; rate per unit of time
Technical or formal expression used in physics, engineering, economics, and similar fields to describe a quantity measured over a standard time interval.
This machine's output is 100 units per unit time.
Measure the precipitation per unit time.
More general 'per hour'; 単位時間当たり is broader and can refer to any chosen time unit (second, minute, etc.) in technical contexts.
Compound of 単位 (unit) + 時間 (time) + 当たり (per). A straightforward technical term.