My (obligatory) tankard (I am after all a bearded traditionalist folky, with pipe, Aran sweater and Laura Ashley dress) has a built-in chromatic tuner. Whenever I want to sing or re-tune I just bash the side and use the note as my reference. The really exciting thing is that depending on how much is left in the tankard, I get a different note. I wonder if that is why I break so many strings.