ABSTRACT
Listing first principles, or golden rules, is a potentially dangerous process – since, by definition, the implication is that there are lesser rules which can be safely ignored, and that is not the case. However, we have to define the issues that must be kept uppermost in the mind of the draughtsman. Some may appear self-explanatory, but I make no apology for their inclusion; when investigating the cause of an error with the benefit of hindsight, it can often seem obvious how the error occurred – clearly, it was not that obvious at the time! Other points may have been touched upon earlier and some may be further developed later.
