And a "Total Service Unit" is........??????
A "Service Unit" is what ANSPs in Europe get paid for (the square root of the result obtained by dividing the maximum take-off weight (in metric tons) of the aircraft by 50, multiplied by the distance flown in 100s of km)
AND
a "Total" is a sum, an amount obtained by the addition of smaller amounts
see
EUROCONTROL - Frequently Asked Questions