Straining at gnats? Trying to define "technical contribution"

I want a definition of technical contribution which will exclude most forms of software. Trickier than it sounds. Here's my best bet so far:

technical contribution

A technical contribution is that part of an invention which cannot be defined as a purely logical or mathematical extension of an existing technical environment because it depends on properties of the physical world which did not contribute to the existing arrangement.

All comments gratefully received.

[Immediate feedback - See the FFII version, which is based on the EP version, at
http://kwiki.ffii.org/UkpoWorkshops0503En]