Like seriously why the hell do they even exist, as if our lives need anymore misery
UMS marks are there so that each exam can be standardised when the raw marks are added together. Obviously some exams are harder than others and sometimes loads of people perform poorly on them, which means the raw marks needed to get an A grade might be slightly lower than the raw marks you'd need in another year to get an A. This becomes quite difficult for students, teachers and schools to work with as it'd be really hard to know "okay, well in unit one you need 56 for a B, then unit 2 you need 55 for a B and then unit 3 you need 57 for a B" as that'd be really confusing if you're trying to work out your overall grade in different subjects. For this reason, the raw marks are then translated to UMS and this is the same each year meaning that if you do a paper marked out of 90 (in UMS) then you'll need the same score to get a B in each of your subjects. When you get into the final stretch of A2s and are trying to work out exactly how many marks you need to get to get a certain grade to meet your university offer, UMS will be much easier to work with than raw marks even though it an added complication at first.