What I interpretate, is that with auto counting of duty, we risk to have double counting, and we want to avoid that somebody having 1 day duty on last day of one Month, and 2 days beginning of the next month will get the duty paid 2 times, although it should be only one time. And so an operator having 1 day at end of month, and 2 days beginning of the other will get 550 / 3 for one month, and 550 x 2 / 3 for the other month.
And so, there will be no change in the amount paid : 550 THB for 3 days duty for operator.
Could you confirm my understanding is correct for these 2 points ?