Sometimes when using Pomodoro Technique I find it real difficult to estimate how long a particular activity will take, i.e., when locating a bug or find out why the webserver won't read my files.
In Pomodoro Technique, every activity should have a time estimate - how many Pomodori I think it will take. Though, this is sometimes impossible! "The problem is solved when I find the bug and since I don't know what the bug is related to, it's impossible to say how much time it will take to find it."
The solution: instead of just writing a number besides the activity, I use the less-than sign (<) before the number, indicating that I have a time-box for the activity, but that it might take less time. If I'm not done when the time-box is over, I have to ask a colleague to help me or ask my boss for extra resources - thus, escalating my problem. Then, I'm forced to have collected some data of the problem to help them to help me. The nice thing is that I still can have most of the benefits Pomodoro Technique gives me, i.e., increased focus when in a Pomodoro and possibility to get "the whole picture" during my breaks. The latter have proved to be an extra nice thing to have during hard problem-solving.
And, if a colleague comes to the rescue, we can construct another time-box, to know when to escalate it further, or at least to notify the team or the boss that we have some nasty problems at hand.
Yet, if I'm collecting metrics of my estimation skills, it is not a very good idea to track data for these bug-fixing Pomodori estimates. Put a "N/A" or a "-" in your records sheet and think for yourself: "Today was an exception, tomorrow will be a bug-free day." And don't forget to do your daily mind-map before you leave for home.