Do not duplicate information when preparing calculations

Duplication of information is a something that needs to be carefully managed when producing calculations. There are times that some duplication helps, for example adding a definition of a value a second time might avoid looking back and forwards in calculations to find the original definition. Generally though you should avoid duplication.

The main reason for avoiding duplication is simple, calculations need to be checked and if you duplicate information, this has to be checked every time you include it. Sometimes this is not too painful, most engineers have committed to memory a reasonable selection of standard references and equations. But often this is not trivial requiring a look up to the original source. So normally, in any given set of calculations, you should only define something once and where you use it multiple times use the reference column to refer back to the original definition (e.g. the page number of the calculations where it was defined).

This principal can be extended further though. Usually on any piece of design, multiple sets of calculations might be involved. Where this occurs, it is often good practice to prepare a Basis of Design document or something similar.  This document can include all common references and even derived information (such as geometric properties of a shape) so that all calculations have a single common source for information. Of course this means that the Basis of Design document will have to be checked with the same scrutiny as a set of calculations but at least it means that the information only has to be checked once.

Don't staple your calculations together

Generally all calculations should still be printable and best practice is usually to print a copy as an original. This copy can then be photocopied and marked up as a check copy giving evidence of the check that has been done on the calculations.

Do not staple hard copies of calculations together because the staples will eventually have to get removed so that the check copy can be created on the photocopier. If there is a chance of the individual sheets getting separated or out of order then job references, calculations references and calculation sheet numbers should be used so that any missing sheets can be identified and tracked down.  

Calculations are always contextual

Calculations should always be treated as contextual; what might work in one circumstance may not be appropriate in another similar but not identical case. You must always think about the problem you are trying to address and what the mechanisms before thinking about which tool or method you should use to calculate the solution.

Automated calculations should be modular

Automated calculations (Excel, MathCAD etc.) should be modular rather than a single integrated sheet. Long calculations tend to have fewer self checks and are more difficult to follow meaning they usually have more signficiant unspotted errors. They are also more difficult to keep up o date when things change because the whole calculation sheet will have to be checked again.

Include commentary

Commentary should be used regularly throughout the calculations to describe the specific mechansim that is being consider at each stage of the calculation. Don't start a check without explaining what mechanism you are checking. Normally you should only check one mechanism at a time, although this does vary depending on the complexity of the problem being considered.

Show free body diagrams

All structural models (from a simply supported beam to more detailed modesl) should have an associated free body or similar diagram. The diagram should be roughly to scale and include all relevant components and forces with dimensions used in the model and forces clearly identified.

Make assumptions clear

If you have assumed an input you should reference it as being an assumed value. If you don't do this then checkers will have to try and look for the source of the information themselves which would be a waste of time if you have assumed it. Make it clear where you have got everything from, even if it is assumed.

Coloured text

Don't use colour and shading in highlighting text in calculations. Calculations are still scanned and sent in black and white and should be formatted so that they can be easily understood in black and white.

Use reference and output columns

Aim for every line of the calculations being either commentary, an input or and process with an output. Using this approach, unless you are writing some descriptive text, every line of calculations shoulc either be an input, in which case it is referenced, or an output, in which case the output should be in the appropriate column of the calculation sheet and highlighted.

Full references

Full references should be included for everything. Don't just quote a book name, but include a full reference to the book along with references to clauses and pages. You will especially appreciate this if you have ever had to search through an entire book to find one equation. 

Cover sheets

All calculations should include a cover sheet giving the context of the calculations. Any reader of the calculations must understand why they were prepared, what was known at the time of preparation and what has been referenced as source material for the calculations. Equally, the QA must be complete, making sure they have been signed off properly, that they are held in the right file for the right project and that nothing is missing.