custom LUA dissector: format display

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Hello,

Lets say I'd like to have a field named ABC which will be 2 unsigned bytes: 0 to 65535 However, the actual value which is represented is -5.0 to 60.0 with linear conversion between the bits to the actual value.

I have some XML which defines the messages and their elements: the name, location, bits value (min & max), actual value (min & max), how it is stored in the database (XML is output from the database), conversion type.

I'm writing some conversion tool from the XML to LUA format. How should I write the dissector so that I'll see values between -5 to 60 ?

Thank you