Within the formula `SCI = C per R`, what is the "per" operation? Should we not write `SCI = C / R` using the "division" mathematical operation?

[patricekrakow]

I found the "formal" usage of "per" as what it seems a mathematical operation quite confusing as "per" is not a well-known mathematical operation.

Is there any reasons why you did not write SCI = C / R, with the well-known "division" mathematical operation?