A chart is a grid of 16 cells per line. A bar in 4/4 is usually 4 cells wide, one per beat, but it does not have to be, and the player works out each chord's length from how much of the bar it fills rather than from a fixed number of beats per cell. In a 4-cell bar in 4/4, one chord alone lasts 4 beats, two chords side by side last 2 beats each, and four chords in a row last 1 beat each.

 

Only the cells the chords occupy are counted, so leading blank beats are skipped: a chord written on beat three of an otherwise empty bar stretches back and sounds on beat one. Fill those beats with slashes to hold the previous chord instead. Entirely blank measures are ignored too. An empty bar is not a bar of silence, and it is not a bar that holds the chord before it: the player skips it. This is the opposite of the way most of us write a chart by hand, where you note the chords only where they change and any musician reads a blank bar as "keep playing the last chord". Write a % in a bar to repeat the bar before it.

 

Chords bunched together do not stop playback. The player reads them, rounds each one to a whole beat, and evens them out across the bar, so you get a rhythm you did not intend rather than an error. Space the chords out so each one occupies the number of cells you want it to hold. A bar can also hold more chords than the meter allows, at most 4 in 4/4 and 3 in 3/4, and the extra ones are dropped from the backing track even though they stay on the chart.

 

Error messages. Pressing Play builds the backing track first, so a problem appears as a message naming the bar. That number counts every bar the player passes through, repeats included. With a repeated 8-bar A section and then a B section, an error in bar 18 is the second bar of B (8 + 8, then 2).

 

For the full guide, see Spacing chords and bars on the iReal Pro website.