Look at an individual feather on your bird. On a single barred bird the feather will be 50/50 colored/not colored. On a double barred bird the feather will be 1/3 colored/2/3 not colored. The not colored will be your white bars. It really is easier to get an idea by looking at pics of male and female Barred Plymouth Rocks since they are more black and white. The male is double barred and the females are single barred.
Penny
Penny