Every time you present to a customer or to an investor—or to anyone whose time or money you want—they are looking for reasons to say “No”. Making a mistake with numbers just hastens that result. If you think about it, unless you are working with an existing customer or investor, your credibility is likely something that you are building from scratch. You may even be starting from within a hole, since you probably had to beg to get a meeting time and, from the attendees’ perspective, “this better be worth it”.
Consequently, when introducing numbers into a discussion or presentation, in addition to mastering the numbers as you talk to them, the numbers need to add up on paper or on the screen.
In fact, as soon as you introduce numbers into a discussion or a presentation, one or more members of the audience will immediately take out their calculators (pocket or mental) and begin looking for ways to poke holes in your reasoning. That’s why it’s also important to be upfront about any major assumptions you are making. These should be also be documented separately.
Numbers need to add up in all directions
When we say that the numbers need to add up, it is worth pointing out that this means in all directions: when you drill down, when you sum up, when you project forward, and when you look backwards to describe historical performance. In all directions. Without exception.
Finally, working with numbers in a presentation tool such as PowerPoint can be a challenge, as it is way too easy to make mistakes when manually transcribing from one document to another. It is best to copy and paste your results from Microsoft Excel, or another spreadsheet tool, and then reformat them as opposed to typing them up from scratch. If you have to choose between fancy tables in your presentation software and validated numbers from your spreadsheet tool, go with the sober yet correct tables copied from the spreadsheet.