How data in bill_data is processed?

Hi !

Historically, we have used Zabbix to collect the bandwidth values of our equipment and calculate the 95 percentile with an annex program. But recently we are considering migrating to LibreNMS. We configured the billing and carried out comparisons. And we realized that there are differences in values between these 2 tools. Attached is a screenshot of the comparison table (on the right Zabbix, on the left LibreNMS).

To tell the truth, I assume that it is Zabbix which is at fault (or the third program which calculates the 95th percentile). But I would like to prove it with concrete elements. So I set out to understand how billing works in LibreNMS. So we come to those for which I question you. I wrote a PHP program which queries the bill_data table of LibreNMS in order to retrieve the data relating to a bill. But the concern is that I don’t understand how to translate the “in_delta” column into a bit in order to be able to achieve my 95th percentile.

At the same time, I would like to understand how LibreNMS processes data from the ports table. What do I need to do to find the bandwidth value shown in the corresponding graphs?
What is the correspondence between column ifInOctets and the IN values of the graph ?