we have unnatural strength - which you think would make opposed strength tests easier - but apparently it only makes your successes better? can someone clarify this for me?

IIRC it just makes your Unnatural Strength modifier go up by 1 for its duration. Basically, x2 goes up to x3.

what I mean is: does my unnatural strength apply to checks at all? or does it just give you more successes when you make a check at your base strength?

It applies to all strength checks. Read the entry for Unnatural Characteristics on page 136.

Unnatural characteristics give the following bonuses to tests:

For normal tests, every multiplier (above 1) makes the test you are taking one degree easier so a X2 multiplier makes a challenging (+0) test ordinary (+10), a x3 multiplier makes a challenging (+0) test routine (+20), and so on up to +30.

For opposed tests, if you succeed you add the multiplier of your characteristic to your degrees of success (DoS). So if you have X2 and if your roll has 2 DoS you add 2 from your Unnatural characteristic for a total of 4 DoS. If you have X3 you would have added 3 for 5 DoS, and so on. If both participants tie on DoS the character with the highest Unnatural characteristic wins. If you fail your test, you get nothing because you've failed.

All of this can be found on page 136 of the core rulebook.

Demonskunk said:

It depends on the ruleset you are using. By standard DH/RT/DW rules Unnatural Characteristics are multipliers for Characteristic Bonuses and also make tests for that Characteristic one step easier for every mutliplier. So what would be a +0 Strength Test for a normal person, would be a +10 Strength Test for an Astartes.

By BC/OW rules, Unnatural Characteristics are flat modifiers (+4 for SB and TB for Astrates) and for every 2 points of Unnatural Characteristic you gain an additional DoS on successful test with that Characteristic.

So both are correct, just depends on which ruleset you use.

Unnatural strength does only seem to make unopposed checks easier (as it decreases difficulty). On opposed tests it doesn't seem to make it easier, which seems odd, but if you think about it makes a significant difference. As soon as they succeed they get two additional degrees of success (for the lowest level), and win on DoS draws, which means the opponent needs to win the dice roll by 30 more. This means with two characters with 45 in a stat the one without an Unnatural Characteristic would have to roll less than 15 if the one with Unnatural Characteristics succeeded at all (and if he rolls under 35 the first guy cannot succeed at all).

The probabilities are a bit too complex for my non-practiced mathematical mind to calculate them.