I am always surprised to discover that many students routinely use tools that they don’t master — or even don’t actually know how to use properly. This is particularly striking when it comes to calculation.

My hands-on way of teaching and the number of numerical exercises we do in class showed me that a very common cause of errors and wrong results is in the last step of solving a problem: doing the calculation. Yes, some students are able to reason properly, apply the right formula correctly, replace variables with the provided data without any problem, and then fail on simply calculating the result. They don’t know how to use the memory registers of their calculator, they vaguely remember something about parentheses and the priority of operations but cannot explain it clearly, and when a result is clearly wrong (given the context), they don’t even see it. And it is even worse if we use a spreadsheet. I could tell you horror stories of students calculating something on their calculator, and then inputting the (truncated) result in the spreadsheet (with a typo on the go), hardcoding values everywhere and generally managing to produce such a messy table that even they cannot understand what they meant the day after.

It happens that recently, at #mainjob, I was asked to produce contents to prepare MBA students for various finance courses. MBA students typically have very different backgrounds, and many did not study business, management or economy before, but medicine, law or engineering, for example. Some never studied some necessary topics such as time value of money, some need a refresher. I took this opportunity to produce a (not so) short handout about calculating properly with the basic tools we have: electronic calculators and spreadsheets. It starts by making sure we have correct basis about how to write properly a given mathematical expression, and then goes to calculating the result, checking that it sounds reasonable, rounding it, re-using it in a later calculation. It is packed with examples and I hope it proves useful in my future classes.

The latest pdf version is freely available, and it is quite liberally licensed (just credit me as author), so feel free to use it in your own classes. I always appreciate a word of comment, suggestions and corrections. If you are a bit tech-savvy, you might even fork the source on github or send me a patch.