It's hard to measure the productivity of any given day. You can of course take a look at your todo list but that ignores the benefit of doing things that are no

It's hard to measure the productivity of any given day. You can of course take a look at your todo list but that ignores the benefit of doing things that are not on your todo list (like hanging out here). I think you should look back at the last 6 months and see if you are satisfied with what you have accomplished. Often it takes a while to realize the benefit of some otherwise unrelated activity (like reading the news or exploring with various libraries). But usually after a few months you'll run across something and be glad you "wasted" some time earlier on that topic. For example I spent a decent amount of time at work (several years ago) researching and playing around with rootkits. This wasn't at all related to my job function at the time. Then one day we had a major breach of security and I wasn't the only person around that knew anything about rootkits, especially how to remove them. I was able to help out and as a result I got a "promotion" (transferred to do security work which was always my passion). Only time will tell if something you learned (or did) was useful or a "waste of time".