Prometheus - get delta between two last consecutive values

Question

I have a gauge metrics that, for instance, gives me a result like this when querying panels_meters[30s] gives me this result:

and a query like this delta(panels_meters[30s]) gives me the differenze between the last value and the value at 30 seconds ago.

BUT I want now the difference between the last two values, independently from the specified time. I just want something like panels_meters[0] - panels_meters[1] assuming panels_meters as an array of data sorted chronologically inverse.

Answer 1

The idelta function is what you want.