About ten years, all in, fulltime - because I read a lot of full articles and took notes on many; I have notes with keywords for over 100,000 articles. (Edit: A

About ten years, all in, fulltime - because I read a lot of full articles and took notes on many; I have notes with keywords for over 100,000 articles. (Edit: Actually ten years probably got me to 250,000+, the rest since that time when I could devote all my time to that one task.)