In the case of the Logic on the left picture, if the power is turned ON and OFF when the variable allocated to the Normally Open is ON and the Timer is operating, the present value would be reset unless both variables of the Timer and the Switch are the retentive variables.

Even if the Timer variable [Timer] is the retentive variable, if the Normally Open variable [Switch] allocated in front of the Timer is not retentive, the Normally Open turns OFF when turning ON the power, and power won’t be passed to the Timer. Thus, the preset value would be reset.

This does not apply for the instructions that operate without electric continuity such as the Timer Pulse, Timer OFF Delay and Counter.