Checking Your Numbers Against Reality
Okay. Last lesson we named things so future-you isn't confused. This lesson is about something a little different. This is about not trusting your spreadsheet too much.
I know that sounds backwards. This whole class is me telling you spreadsheets are handy and worth learning. And they are. But here's the thing nobody tells you when you're starting out.
A spreadsheet will give you a wrong answer with total confidence. It doesn't hesitate. It doesn't say "hmm, this seems off." It just shows you a number and sits there looking correct, whether it is or not.
So you have to be the one who checks.
The story I have to tell you
Sooo, about three years ago, when I was rebuilding the inventory tracker at the warehouse, I had a formula that was supposed to add up a product line across a few different tabs. Looked fine. Ran fine. Gave me a total.
The total was wrong by about 300 units.
Not a little wrong. A whole pallet's worth of wrong. And I didn't catch it. My boss did, because he happened to walk the floor and count boxes that same week and the number in his head didn't match the number on my screen. If he hadn't done that walkthrough, we would've made ordering decisions off a fake number. That's not a small mistake, that's a "we bought too much of one thing and not enough of another" mistake.
I still remember exactly where I was standing when he told me. Not a fun afternoon. 🙈
The formula wasn't even that complicated. It just had one cell reference pointing at the wrong range, so it was missing an entire section of rows. Sheets didn't know that was wrong. Sheets just did what I told it to do, which is the whole problem with spreadsheets in one sentence. They do exactly what you tell them, not what you meant.
So here's my rule now
Check your numbers against reality. Every time.
That means, if your spreadsheet says you have 240 units of something, you actually go count. Or at least count a sample and make sure it's in the ballpark. If your spreadsheet says you made $4,200 last month, you look at your actual bank total and see if that number is anywhere close.
You're not re-doing all your math by hand. That defeats the point. You're spot-checking. You're asking "does this feel right" before you act on it.
How to actually do this at home
Pick one number that matters to your business. Total inventory, total sales for the month, whatever you built a formula for in the last couple lessons.
Step one. Look at what the sheet says the answer is. Write it down or just keep it in your head.
Step two. Get the real-world version of that number, however messy that is. Count the actual boxes on the shelf. Log into your actual bank account and look at the actual deposits. Pull out receipts if you have to.
Step three. Compare them. If they're close, great, you're probably fine. If they're way off, something's wrong in your formula, not in your business. Go find it before you make a decision based on the wrong one.
A good habit is to do this check at the start or end of every month, even once things are running smooth. Not because you don't trust yourself. Because everybody's formulas drift eventually. Somebody adds a row in the wrong spot, a range doesn't update the way you assumed, whatever. It happens to me and I've been doing this three years.
A quick note on where errors like to hide
The mistake I made lives in a specific spot, so keep an eye on:
- Ranges that don't update when you add rows. If your formula was written to sum rows 2 through 20 and you add new data in row 21, it might not get counted. Sheets is supposed to expand these automatically sometimes, but not always, and I don't fully trust it to.
- Tabs that look similar but aren't the same. If you've got a few product lines split across tabs, it's easy to reference the wrong tab and not notice, because the formula still runs and still gives you a number.
- Totals that seem a little too round or a little too clean. Real business numbers are usually a little messy. If your total looks suspiciously tidy, poke at it.
None of this is about being paranoid. It's about knowing the spreadsheet is a tool, not a witness. It didn't see your inventory. It doesn't know your bank balance. It just does math on whatever you fed it, and if what you fed it was wrong, it'll hand that wrongness right back to you looking very official.
Before next time
Pick one number from your own sheet, whatever you've built so far, and go check it against something real. A shelf, a receipt, your actual bank app. See if it holds up. If it doesn't, that's not a failure, that's exactly the kind of thing this lesson is for.