If your use of a value in units lives for so long as for it to not be clear in what unit it is in or should be in (eg. spans more than 20 lines of code), I thin

If your use of a value in units lives for so long as for it to not be clear in what unit it is in or should be in (eg. spans more than 20 lines of code), I think you've got a bigger problem with code encapsulation. I think the practical problem stems from widespread APIs which are not communicating their units, and that's what we should be fixing instead: if APIs are clearer (and also self-documenting more), the risks you talk of rarely exist other than in badly structured code. Basically, instead of having `sleep(wait_in_seconds)` one should have `sleep_for_seconds(wait_time)` or even `sleep(duration_in_seconds=wait_time)` if your language allows that. But certainly use of proper semantic types would be a net win, but they usually lose out in the convenience of typing them out (and sometimes constructing them if they don't already exist in your language).