In case officials, non-regular officials and clerical helps (hereinafter to be called personnel) in the service of Regional Financial Bureaus or taxation offices, make an official trip for more than 5 hours per diem for purposes of carrying out investigation, examination or recovery of arrears, or assistance thereof regarding the national taxes by order of the chief of the competent authorities, the Government may, per day of trip, pay them the special allowance the amount of which is to be computed by applying the following ratio to 1/25 of the total amount of such regular monthly salary or compensation and monthly allowance prescribed by the Minister of Finance as may be given to the personnel: