Adding values from diff() to trigger description

[Karl_MCS]

Good afternoon,

I have a very simple trigger expression:

{Template SNMP Brocade:snChasUnitSerNum.[{#SNMPINDEX}].diff()}

And this is working fine, however I would like to add the two values used in the diff() to the description. I have tried this:

Previous serial number: {{HOST.HOST}:snChasUnitSerNum.[{#SNMPINDEX}].prev()}
New serial number: {{HOST.HOST}:snChasUnitSerNum.[{#SNMPINDEX}].last()}

... but these do not resolve in the description. I also tried using a different expression with .prev() <> .last() and pulling the {ITEM.VALUE} and {ITEM.VALUE2}, however this was unable to evaluate because they are strings instead of numbers.

What's the way to do this?

Thanks