Complex sentence: They often represent a single capability of the character such as the weight characters can lift or the pace they move at, and are either unitless numbers or they will usually use real-world units of measurement (such as kilogram or metre per second).
Split into simpler sentences: They often represent a single capability of the character such as the weight characters can lift or the pace they move at. Some are unitless numbers, but more often they use real-world units of measurement (such as kilogram or metre per second).