Custom Performance Monitor - How to define NumericToString type?

Custom Performance Monitor - How to define NumericToString type?

I'm trying to create a custom monitor where the function expression is set to NumericToString, are there any guides on how this needs to be setup? The OID returns a value between one and 7 and I want to assign text strings to be displayed. Does this type actually do what I need? or does it simply convert the numeric 5 to a string "5"?

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