Danny. I agree about the capo. So if you can play in Bb you should definately do it. I am basically lazy! Finding the key from the last key ain't gonna work if you trying to play along with the radio ( as grinch mentioned). I usually just strum along with E shaped bar chords up and down the neck or pluck a single string. You soon hear that the key is usually the chord or string that sounds the rightest (is that a word?) and then you can happily play along with the rest of the song with I IV and V (usually). It may not be right but the next song will be better.

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