[growse]

This feels like semantics. If a counter repeats a value, it's effectively gone backwards and by definition is not monatomic.

A delta between two monatomic values should always be non-negative. This is not true for Unix time.

[wat10000]

“Monotonic” means non-decreasing (or non-increasing if you’re going the other way). Values are allowed to repeat. The term you’re looking for is “strictly increasing.”

[growse]

I guess this hinges on whether you think Unix time is an integer or a float. If you think it's just an integer, then yes, you can't get a negative delta.

If, however, you think it's a float, then you can.