Graphing non-standard snmp queries

[ptera]

The device I am trying to graph traffic used requires me to call snmp get that are not under the snmp interfaces. I have to pull the current bytes then 60 seconds later call it again and then subtract the two. I can pull the number values using SNMPv2 agent type for the items.

Key = channelInternalRxBytes.11.0.
SNMP OID = .1.3.6.1.4.1.15397.2.2.25.1.3.1.11.0
These work and can be graphed but will not show usage.

So then I try to use a type Calculated
Key = CurrentTrafficRx
Formula = ("channelInternalRxBytes.11.0.")-last("channelInternalRxBytes.11.0.")

But I obviously do not know what I am doing because I get the error message.

Cannot evaluate expression: expected numeric token at ""channelInternalRxBytes.11.0.")-96618521149442"

Thanks

[ptera]

Update

Got rid of the error with the following...

last("channelInternalRxBytes.11.0.")-last("channelInternalRxBytes.11.0.",2)

But returned value is zero. ?!?

[ptera]

Well here I am over a year later - still trying to solve this problem - found this thread while searching for an answer.

Bummer that there is no answer yet even with version 3.4 :-(