Rank
A characters rank is determined by comparing the intelligence and charisma to a set value.
 If the sum of intelligence + charisma is greater than 25 (IQ + Char > 25), then roll 1d10 to determine whether the character is an NCO or officer. A modifier equal to intelligence x .1 (round up) can be added to the die roll.
 If the final number (with modifier) is greater than 7, the character is an officer; otherwise the character is an NCO. Roll 1d10 again to determine the final rank, including the modifier. If the sum is less than 25 (IQ + Char <= 25), then roll 1d10 with no modifier.
Example

Our character has a combined intelligence and charisma score of 12, which means he gets a roll of 1d10 with no modifier.

Assuming he rolls a 5, we look at the chart below (labeled “combined score <= 25”) to see that his rank is Corporal.

If our character did have a score greater than 25, then he would roll 1d10 with a modifier of 1 (IQ x .1 = .7, rounded up to 1) and he would be ranked in the chart labeled “combined score > 25”. Again assuming he rolled a 5, his modifier would add 1 to it giving a final value of 6. This isn't greater than 7 so he is an NCO. Assuming another roll to determine his NCO rank, he gets a 8. With his +1 modifier, his final value is 9, resulting in a final rank of Master Sergeant.

If we assume he did get a final value of 8 or greater, then his final rank is found on the Officer chart; if we use the previous value of 9, then his final rank would be Captain.
Final Rank(including modifier)  Combined Score <= 25  Combined Score > 25  

NCO 
Officer 

1  Private  Staff Sergeant  2nd Lieutenant 
2  Private First Class  Staff Sergeant  2nd Lieutenant 
3  Lance Corporal  Staff Sergeant  2nd Lieutenant 
4  Lance Corporal  Staff Sergeant  1st Lieutenant 
5  Corporal  Gunnery Sergeant  1st Lieutenant 
6  Corporal  Gunnery Sergeant  1st Lieutenant 
7  Sergeant  Gunnery Sergeant  1st Lieutenant 
8  Sergeant  Gunnery Sergeant  Captain 
9  Sergeant  Master Sergeant  Captain 
10  Staff Sergeant  Master Sergeant  Captain 
11  N/A  Master Sergeant  Major 
12  N/A  Sergeant Major  Major 