I've recently created an excel spreadsheet that easily calculates GPA in both 12.0 and 4.0 scales rather than having to do it manually after each term. It also has a nice graph that shows how your GPA has changed after each term. I think this could be useful to a lot of students so feel free to try it and tell me what you think!
*Note* There's only 2 columns with information you have to manually enter, the name of the course and the final grade you received (# from 1-12). The number of units for each course defaults to 3 but you can change that by just typing another number in that cell. Everything else is completely automatic and works according to the average calculation and conversion chart posted on the McMaster site.
What it looks like blank
...and with some arbitrary data
Hope you find it useful! Please let me know of any issues or problems with the tool.