expressing or that expresses

[Tukanja]

Dear friends, which of these two sentences is OK. If both of them are OK which one do you prefer and why?

This is a number expressing the relative effect of "something" on the "something else" for a specified standard subgrade category (by XXX).

This is a number that expresses the relative effect of 'something" on the "something else" for a specified standard subgrade category (by XXX).

Thanks

[Josef]

It's impossible to answer sensibly without knowing the full context - specifically and at least the preceding sentences or the entire paragraph.