I'll point out the same things that I have throughout the thread:
But before I start, look at
this .pdf. Most people talk about 'scaling', and have no idea about how it fits into the process. After you've looked at that, come back and read this.
1. Scaling is a mathematical process. It is exact,
2. primarily, scaling essentially takes into consideration one's place in one's school grade, and then one's grade in one's candidature. Also, there are a number of other mechanisms in place. But essentially, to offer a reasonable estimate, I'd need to know what school a student goes to and where the student is placed within his/her year,
3. like the year's UAIs themselves, scaling for a year cannot be exactly calculated before that very year itself. This is because the scaling process differs from year to year and and is decided based on the candidature (changes from year to year), the marks spread (changes from year to year), and several other things,
4. Bored of Studies' own
calculator is one way a student can estimate how x marks will contribute to his or her UAI. Similar programs include JUAI. Speak to your careers advisor. However, they cannot be exact because of the mechanism described in 3,
5. Worrying about subjects' scaling is futile: Firstly note that you will do better in subjects which you prefer. Secondly, note that worrying reduces ability to think clearly - worrying about scaling will not help you in the long run. Thirdly, why not note the (small) differences between your subjects' contribution to your UAI? Considering each subject contributes a maximum of 1/5 to your UAI, even subjects with large scaling 'differences' (technically, differences at one point) may have little eventual impact on your UAI.