Time Period on C.R.O.
Display Screen is 10x8 grid. The vertical grid (Y-axis represents voltage) is divided up into 8 (major) divisions and the horizontal grid (X-axis represents time) is divided into 10 major divisions. To improve the precision, each of these divisions is further broken up into 5 minor divisions.
Volts/Div control lets us change how many volts are represented by each vertical increment of grid (vertical axis) on screen.
Correction: If Time/Div control is set to 1 ms/div, it implies that each major horizontal division is 1 ms whereas each minor horizontal division is 0.2 ms. In other words:
Reading of Time = (number of divisions) x Time/Div