Because you've only done one speaking assessment. Writing and speaking are marked out of 60 each, so each controlled assessment is marked out of 30. So say if you got 25/30 in your one speaking, that's an A but because both marks are combined, it's 25/60 which is worth 38 UMS and is an E grade. If you got 26 and 24 in writing, that's 50/60 which is a B and worth 70 UMS. You need 270 UMS overall to get an A*. The highest amount of UMS points you can get from a listening or reading paper is 60. So if you got 60 on both papers, that would give you 120 UMS, but if you added that to your controlled assessment you'd have 228 UMS, which is a B.