In this instance, a visible bar is equal to 16 pattern rows (ticks). This means that a pattern (indicated by name) placed in a column, would take 16 pattern rows to scroll through this one bar.
A bar may be
equal from anywhere between 1 and 256 pattern rows, allowing you to
view entire songs or pieces of songs in one screen, rather then
endless screens.
Note: when you change the step value from for example 16 to 12, all the patterns that are placed in the sequence on places other than 0, 12, 24, 36, 48, etc. (amounts of ticks), will not be displayed anymore. To get them back on your screen, change the step value back to 16.