"Expert" is a tricky word, and I only know how to measure this in relative terms. For a given area, I know I have a high degree of expertise when colleagues wh

"Expert" is a tricky word, and I only know how to measure this in relative terms. For a given area, I know I have a high degree of expertise when colleagues who are working in similar areas begin to regularly ask for my help. That doesn't necessarily say anything about my abilities relative to a different population: I know a hell of a lot about image analysis relative to the other engineers in my group, but I know there are plenty of people who can kick my ass in this. I suppose I might also measure this based on my own need for assistance, i.e. I am an "expert" when I only rarely need to turn to colleagues or the literature for help. But this isn't a very functional definition for me, as I strongly prefer to be working at the edge of my knowledge; thus I am almost always in conversation with others who know more than me.