For most courses, SOAS doesn't give you a final classification based on an average mark, but is based on the amount of classifications you have. If you have half or more units of a certain classification, you will get that classification, unless you have two or more units of two classifications below that, which can bring down your overall grade by one classification. Conversely, this can work the other way around, so two units that are two grades above your average can bring up your grade. So for example, if you had eight units, and four were a first, you'd get a first, as long as you don't have two or more units that were a 2.2. If you did, your grade would be dragged down to a 2.1, as one of the four firsts would be 'cancelled out' and only count as three firsts instead of four, but if you only had one unit at a 2.2 and the rest were 2.1s, you'd get a first. Also, if you had five firsts and two 2.2s, you'd still get a first because one First would be cancelled out, still leaving four of eight.
It might look confusing, but it has logic, although I still don't like it as it doesn't account for example, if you had three units or so at 68 or 69 - it would make no difference if these units were 60 or 61.