|You literally have written a book.
|7 - 9
|Expert, go-to person on this technology.
|5 - 6
|Solid daily working knowledge. Highly proficient.
|3 - 4
|Comfortable working with this, have to check manual on some things.
|1 - 2
|Have worked with it previously but either not much, or rusty.
I copied this grading scale mechanism from a failed Google interview ;-)
One problem with it is that I am always very hesitant to put a 5 on anything, who can not look at the documentation?
It is also hard to scope things right. Who can claim to be a C++ or Linux kernel expert, even if you wrote a book about it, since those are such humongous topics?
As a result, I haven't updated this in a while, and things may be out of date.
If your project does something that interests me, I can what it takes to contribute. Tell me what I must know, how long I have to learn it, and I'll call you back when I've mastered it.