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•84 The 100 Greatest Business Ideas of All Time

It may be slightly esoteric to make a direct link of the work of Turing with the
modern day spreadsheet, but the argument has some merit. Essentially spreadsheets
allow the user to mix data and logic in a way that reflects how most managers think
and plan their businesses. Creative thought and intuition can be quickly tried out at
an overall level, formalised and developed according to the answers found to a series
of ‘what if’ questions.

This flexibility makes spreadsheet modelling ideal for managers to analyse a
specific situation in a specific way. You can start where you like, for example from
sales or fixed costs. You can check that some variables in the middle of the model
stay within precisely or loosely defined parameters. You see the result of any for-
mula as you enter it. This makes it likely that you will detect errors early. It also
means that you can pause after each step to recognise what you have learnt before
moving on.

Opinions vary as to whether spreadsheets are efficient if you take them out of
this personal environment and build models intended to be run corporate wide.
Intuitively I doubt it.

Experienced modellers volunteer the following tips to help newcomers wield
the power of the spreadsheet.

1 Build it step by step. Make sure one month is doing exactly what you want
before copying it eleven times.

2 Build the assumptions table outside the model. This means that the top of the
spreadsheet has the assumptions that you are going to test, and further down is
the actual model.

3 Check each formula as you enter it. Since the assumptions are separate from
the model it is easy to enter new assumptions and check their impact on the
formula before moving on.

4 Check the overall model by seeing that it behaves as you would expect when
you give it new, or even extreme, variables.