Introduction

The purpose of this chapter is not to show you how to write formulae in the first place, but to consider ways in which you can set them out more clearly and which conform to the principle of error reduction. One of the concerns we have about writing calculations is what I call the 'intellectual challenge' approach: the attempt to solve modelling problems in the least amount of space. The results are formulae of bewildering length and complexity, that require considerable time and effort to understand, and are difficult to audit and review. We have all done it we have spent some time trying to solve a problem and in so doing we have created a monster of a formula, which takes up four lines on the formula bar and has six closing brackets. And then we look back at the formula a week or so later and amaze ourselves that we were so clever, because we are not quite sure how (or why) we did it.

There are a number of articles and web sites whose authors push hard for this approach. In almost every case I would urge caution, because long, complex calculations are daunting to look at, and the operational research suggests that the longer the formula, the less chance of it being either read correctly or understood. If the reviewer or user is unable to understand a formula, we are failing to give them the confidence they need to rely on the results of...