Generally in manufacturing units push buttons are commonly used in switching on or off the devices. Push buttons have one inherent characteristic that they cannot retain their position i.e. one has to constantly press the push button in order that the machine gets and remains started. Moreover, if this condition is not met the device with constantly flicker causing damage to the machine.
Toggle switches are another option which can be used for this purpose. The main advantage with them is that they can retain their position which the push buttons could not do. Toggle switches need to be operated in order to change their position. Thus we can turn on the switch and rest assured that the machine is working. But this causes a problem in industries, as the same switch will have to be operated again in order to switch off the machine. Logically with the help of ladder logic it will not be switched off.
In order to remove the disadvantage of pushbutton a solution internally in the ladder logic in PLC has been given in the form of instruction by many manufacturers of PLC. This is latch and unlatch or set and reset instruction.