The 1X points and 9X points are calculated differntly. Search for Trazora's detailed explanation in the DBS Altitutde Thread - I think he wrote it there last time.
I'll try my best to explain.
In your monthly statement, you will see a column Earned/Adjusted. This actually shows the 1x points for all your spending in this STATEMENT (note: NOT calendar month), PLUS the 9x points for the previous CALENDAR MONTH.
The formula to calculate 1x points is (where $$ is the spending):
=ROUNDDOWN(($$/5)*1,0)
The formula to calculate 9x points is (where $$ is the spending):
=ROUNDDOWN(($$/5)*9,2)
The 9x points for the previous CALENDAR MONTH is summed up then rounded down to nearest whole number before being added to the 1x points for this STATEMENT and reflected in the Earned/Adjusted column.
To give an example, I get my statement on the 27th of every month.
For September statement:
Spending / 1x points / 9x points
29 Aug - $172.57 / 34 / 310.62
5 Sep - $82.89 / 16 / 149.2
For October statement:
Spending / 1x points / 9x points
26 Sep - $156.15 / 31 / 281.07
4 Oct - $115.5 / 23 / 207.9
So for my October statement, the 1x points will be 31 + 23 = 54 and the 9x points will be 149.2 + 281.07 = 430.27, and the points listed under the Earned/Adjusted column should be 54 + 430 = 484.
I hope this was clear!