# What is the exact fomula of the funtion rate?

I use the folowing metrics :

rate(fuelBurningTime{job=“Raspberry”}[\$__rate_interval])

but i did not found in the documentation the exact calculation done by this rate function.
Il mathematics I understand rate as dervative.
But question is what is the interval used? is ther many point inside this interval ?
Is there parameter to control it more?

For exemple If I want to calculate the “n value” - “n-1 value” / interval ?
how can i do that ?

Many thanks

Hi @ewok2,

The `\$__rate_interval` variable is meant to be used in the rate function. It is defined as max( `\$__interval` + Scrape interval , 4 * Scrape interval ), where Scrape interval is the Min step setting (AKA query interval, a setting per PromQL query), if any is set, and otherwise the _Scrape interval as set in the Prometheus data source (but ignoring any Min interval setting in the panel, because the latter is modified by the resolution setting).

There’s a really great blog written when the \$rate_interval feature was released that helps with some examples of the problems it solves and how it works:

Thanks for reply.
Indeed I found a lot of information on the difference between \$__rate_interval and \$_interval.
Initialy I was using \$_interval with some trouble when selecting a short interval.

But my question is more on the rate function itself.
I need to calculate the Delta between 2 mesurment,and I have the feeling that rate function is more complex than taht?
maybe there are another way to get the delta divided by the interval of theses 2 points?

Hi @ewok2,

Depending on your use case, you could also consider `delta`, `idelta`, or `increase`(not adjusted per second like rate), all of the functions and what they do are explained in the prometheus query functions docs:

Thanks for the link but there is something I did not understand…
I have a kWh value that I monitor.
When I plot a graph in grafana with this query in a time series :

ClimConsumptionVal{job=“Rasp-Cave”}

in the last 7 days I pass from 690 kWh to 694kWh
When I try to display a “stat” with the following query (with a selected 7 days periodes) :

delta(ClimConsumptionVal{job=“Rasp-Cave”}[\$__interval])

I get 4 kWh which seem’s Ok
but if I try this query instead :

delta(ClimConsumptionVal{job=“Rasp-Cave”}[7d])

I get 7MWh ???

I think there is something I do not understand…
Any idea of what?

Do you really have the \$ in your 7d interval?

Sorry a typo here but not in graphana
With [7d] I have 7MWh…
(I have corrected the above post)