To build good models, we have to think like product designers.
"Form follows function" - Louis Sullivan (architect)
"Design is not just what it looks like and feels like - design is what it does" - Steve Jobs.
Whether we are aware of it or not, we constantly make design decisions when building a financing model.
Product designers think about their intended users. They design for that person. What job is that person trying to do? What will make that job easier or more difficult?
As modellers, we also have to think like product designers.
If form follows, function, what functions does our model need to support? If good design is also what it does, and not just how it looks, what do we need the model to do?
Financial models are a bit like cars. Car design has to cater to the requirements of three different user types:
- Drivers: Clarity of information, easy access to controls, standardisation
- Passengers: Comfort, space, light, view, entertainment.
- Mechanics: Ease of maintenance, access to essential engine parts, useful diagnostic information
In the case of models, we don't have passengers. We're designing for drivers and mechanics, model users and model builders.
Designing presentation vs calculation sheets
The design requirements for presentation sheets are different from calculation sheets.
With presentation sheets, we want to apply the best data visualisation techniques to ensure that critical data is clear, accessible and well presented.
Calculation sheets are more like the engine of the model. We are designing for ease of maintenance; we want to make it easy to change calculations, add new model sections, remove unused code etc. These are not presentational requirements. The things we might do to "prettify" calculation sheets often act against the interests of efficient model update. I often see modellers conflate these two things and try to turn calculation sheets into presentation sheets. The results are sometimes pretty. They are rarely helpful.
In the following chapters, we'll look at model structure. To begin with, we'll focus on the design of calculation sheets. Our design focus in these sheets is on the model builder.
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