Expressing Rates & Ratios in IT English

"Cache hit ratio" (or cache hit rate) is the standard term. It measures the proportion of requests served from cache vs. total requests. "Score" and "level" are not standard IT metric terms here.

"Per" is the standard preposition for rates: "requests per second (RPS)", "errors per minute", "transactions per second (TPS)". All these follow the pattern: [count] per [unit of time].

All four options are grammatically plausible, but "across the whole period" is the most idiomatic for distributing a total metric across a time span. "Over the whole period" is also common. "During" and "within" are slightly less natural in this phrasing.

"Ratio" is correct for LTV:CAC (lifetime value to customer acquisition cost). Ratios compare two quantities using "to 1" or colon notation. "Rate" implies change over time; "score" and "index" are not used here.

"Out of" is the natural phrasing for fractions/proportions: "3 out of every 1,000 requests". "Per" works for rates expressed over time units (requests per second), but "out of" is idiomatic for part-of-a-whole expressions.