Look at any results slip and you will see that an AS qualification has a maximum of 300 marks from the three different AS units.

In some subjects, the three units will be worth 100 marks each. In others, the marks available for each unit are slightly different. This is also the case for A2 units.

Each exam paper is unique and so the difficulty of the exam may vary slightly from year to year.

Senior examiners in each subject judge the difficulty of each paper by looking at a sample of candidates' work and exam papers from the current year and from previous years, examiners' reports and statistical data.

They use their professional judgement to decide on the grade boundaries for each paper, using what are called 'raw marks'.
For example, you might need 40 raw marks out of 50 for an A grade one year, but 42 out of 50 the next, depending on the
difficulty of the paper.

To make the unit results compatible and comparable (so that they can be added together to get the final grade, even if they were taken at different times), raw marks from the examiners are converted to points on the uniform mark scale (UMS).

What is the UMS?

On the UMS, the range of marks for a particular grade is the same each year (unlike the range of raw marks for each grade). The raw mark grade boundaries are translated into fixed points on the UMS. The range covered by the UMS varies between units. For a unit with a mark out of 100, the ranges of UMS marks for each grade are:

• E: 40-49
• D: 50-59
• C: 60-69
• B: 70-79
• A: 80-100.

For example, if the examiners decided that a raw mark of 90 out of 120 on a unit was the lowest mark for an A grade, then that 90 raw mark would become 80 when translated into the UMS mark out of 100. If your raw mark lies between the A and B grade boundaries, the proportion of marks you get within the range for that grade is calculated.

If the raw mark needed for a B this year was between 80 and 90 and you got 85 marks, you are halfway up that range. Your UMS mark is then halfway up the 70-80 UMS range, which equals 75 marks. (The score conversion diagram might make this clearer.) The UMS marks for individual units are then added together to give an overall UMS mark for the subject as a whole. The maximum total UMS mark is always 300 for AS levels and 600 for A levels.

Score conversion diagram

	Raw mark	UMS mark
Full marks	120	100
A grade	90	80
Your mark	85	75
B grade	80	70