Not sure if your looking for feedback, but it needs to be a bit more complicated.
So split into years, modules and assignments+exams
For me year 1 is worth nothing, year 2 is worth 1/3 and year 3 worth 2/3 and then within that i have 8 modules each year with varying numbers of courseworks.
In order to use your calculator i have to do a lot of additional maths - making it relatively useless. If you could incorporate what i have mentioned above, and then maybe a "what grade do i need to average in the rest of my exams/courseworks to get a 2.1/1st etc" feature, that would be pretty cool