Watch the Counting Measures online guitar lesson by Rich Maloof from Acoustic Guitar For Beginners
Picking up on our two-measure example from the last clip, here's a closer look at a full four measures (bars) of music. Popular music is very often broken up into 4-bar sections or "phrases." It's a balanced amount of time for a chord progression to go by.
Our previous examples have been showing one chord per measure (sometimes the same chord is held out over several measures at a time). Now we're subdividing a measure. The 4th bar in this example includes two chords (Am and D).
Rhythm notations will sometimes show you where exactly to change chords. When a "strummy" song shows two chords in one measure, you can simply divide the measure evenly in half so that each chord gets two beats.