What we will do about overlapping counters?

I think we maybe need two operators here: difference to previous one and rate. I am not sure if this is exactly the same. Because rate has a time component. And difference can be used only where you have a counter value as input, but you are interested in how much new has been added from previous one. The difference is also that in rate you have missing values if you don't have exactly both values, current and past, but in difference you don't care when was the previous value, just how much is the new value at a given time. No?