Newbie - SNMP Wan Interface daily throughput graph

[supertramp4]

Hi, I am new to Zabbix, and using version 6.4.6 have successful started to monitor our main router to get the Bits received using the key net.if.in[ifInOctets.10002]
As these values are cumulative, i would like to have a calculation that converts the data into relative values.

so for example from the latest monitored data
Time Bits
Tnow : 2023-09-20 10:33:30 = 1349718079440
Tprev : 2023-09-20 10:30:30 = 1349527019071

so the calculation i need is
Delta change = (Bits[Tnow] - Bits[Tprev) / (Time[tnow] - Time[Tprev] )
Delta change = ( 1349718079440 - 1349527019071) / (2023-09-20 10:33:30 - 2023-09-20 10:30:30 )
Delta change = (191060369 ) / 180) ( note convert 3 mins into seconds)
Delta Change = 1061446.494 Bits/Sec or 1036kbps

The purpose is to be able to display a more conventional daily graph that our router displays like


Can anyone point me in the right direction to create a graph like this.
Many thanks

[cyber]

But you can add preprocessing "change per sec" ...

[cyber]

But you can add preprocessing "change per sec" ...

[supertramp4]

Perfect - Thank you. Its obvious once you know where to get the answer !