Add Error margin in the metrics output / exporter

[damienfernandes]

Problem

In prometheus, we don't scrape error margin for collected impacts values.

Solution

To be able to explicit result, I will be interesting to add error margin and be able to display it in grafana. Absolut Unvertainty will be calculated with rawdata bloc (min, max, value) for every impacts

Alternatives

Investigate if we add new metrics or we change value metrics to scrape Value ± Absolute Uncertainty

Additional context or elements

Absolute Uncertainty

[damienfernandes]

@demeringo To provide scientific rigor when presenting experimental results 🧪

[demeringo]

I fully agree that returning the uncertaincy is important.

I think we need to do 3 things:

• update the internal data model to add an uncertaincy field to each value.
• create an xxx_absolute_uncertaincy metric for each existing `xxx metric (except maybe for the exact counters like number of instance etc...)
• ... then calculate this uncertaincy using min and max values returned by API