If you’re using a mac and os x you’ll probaly love spotlight search (use cmd+space to bring it on).
What you maybe did not recocognized is the fact spotlight can even calculate für you. A few examples:

calculate with spotlight 1

Simply use the well known operators + (plus), – (minus), * (multiplication) and / (division)

calculate with spotlight 2

Furthermore you can calculate radicals by typing sqrt()

calculate with spotlight 3

Your mac even knows pi.