Sets the number of small ticks.
I this case bellow then we are representing zero to 5 Volts. Setting large ticks to 6 is good option in this case since then each large tick represents 1 Volt.
By choosing 4 small ticks, then each small tick represents 0.2 Volt, where you have 0.2 + 0.2 + 0.2 + 0.2 V = 0.8 V and the last 0.2 is covered by the large tick making it = 1.0 V.
Ticks explained: