This is in relation to the numerical question type.
Since Moodle 2.0, you can have it so that the student gets partial credit if they answer with the right numerical value, but with the wrong unit.
That sounds so simple doesn't it? Sadly it isn't to start to get a glimmering of the type of problem that is possible, here is a slightly artificial example:
Question: "A circle has a radius of 0.00005km, what is its area? (remember to give the correct unit)"
Accepted units: cm2 or m2
What answers would you consider to be "Right numerical value, wrong units" and why?
If you wish to cheat, you can read the discussions in MDL-27418 and MDL-28118, but it would be more useful (I think) if you try to answer before you read that.