When using the PLS function with a time base of 1 sec, and you want 50% duty cycle, you must use a preset of an even number. If you use an odd number the OFF cycle will be one second longer than the ON cycle. If you need to use a odd number, say 5, change your time base to 10ms and use a preset of 500. The PLS function will then give you a 250 ms ON and 250ms OFF cycle time.