Your AI and Your Data: Don't Let It Make Up the Number
No AI number reaches your report until it passes three questions: what a row is, what it divided by, and what it left out.
You go at your own pace, with your Maestro beside you, 1:1, through the whole course: ask it anything, and it asks you questions too.
15 skills · 5 modules
What will you be able to do?
Each box is a skill. The base is at the bottom, recognizing and explaining, and you work your way up to building something of your own and judging what works and why. Hover over a box to see what it builds on. Click it to see where I teach it and how your Maestro checks it.
- Evaluate
- Synthesize
- Analyze
- Apply
- Understand
Evaluate
Audit a complete AI answer with the three questions
Where I teach it: Ask for it right, then decide · How do you check a full summary an AI wrote?
Builds on:
- Diagnose an average computed at the wrong grain
- Compare groups with rates, not just counts
- Detect rows that were left out of a result
- Detect duplicate rows and measure how much they inflate a total
Your Maestro asks you to judge when it fits and why and saves it as evidence when you do.
Decide how much to check a number based on what is at stake
Where I teach it: Ask for it right, then decide · When can you trust a number from an AI?
Builds on:
- Audit a complete AI answer with the three questions
- Explain why an AI's number needs checking
Your Maestro asks you to judge when it fits and why and saves it as evidence when you do.
Synthesize
Design a question whose answer can be checked
Where I teach it: Ask for it right, then decide · How do you ask an AI for a number you can check?
Builds on:
- Explain why an AI's number needs checking
- Identify the denominator of an average or percentage
- Detect rows that were left out of a result
Your Maestro asks you to build something of your own with it and saves it as evidence when you do.
Analyze
Diagnose an average computed at the wrong grain
Where I teach it: What a row is · How do you calculate the average ticket when one ticket spans several rows?
Builds on:
- Count at the grain the question asks for
Your Maestro asks you to break a problem down with it and saves it as evidence when you do.
Detect rows that were left out of a result
Where I teach it: What it left out · Why doesn't the AI's table add up to your file's total?
Builds on:
- Explain what happens to empty cells in a calculation
- Recompute a number an AI gave you
Your Maestro asks you to break a problem down with it and saves it as evidence when you do.
Apply
Recompute a number an AI gave you
Where I teach it: Before you believe it · How do you recompute an AI's number with pandas?
Builds on:
- Read a short pandas calculation
Your Maestro asks you to use it on a new case and saves it as evidence when you do.
Count at the grain the question asks for
Where I teach it: What a row is · Is counting rows the same as counting sales?
Builds on:
- Identify what a row of a table represents
- Recompute a number an AI gave you
Your Maestro asks you to use it on a new case and saves it as evidence when you do.
Compare groups with rates, not just counts
Where I teach it: What it divided by · Count or rate? How to compare groups of different sizes
Builds on:
- Identify the denominator of an average or percentage
- Recompute a number an AI gave you
Your Maestro asks you to use it on a new case and saves it as evidence when you do.
Detect duplicate rows and measure how much they inflate a total
Where I teach it: What it left out · How do you find duplicate rows that inflate a total?
Builds on:
- Identify what a row of a table represents
- Recompute a number an AI gave you
Your Maestro asks you to use it on a new case and saves it as evidence when you do.
Understand
Explain why an AI's number needs checking
Where I teach it: Before you believe it · How do you know if the number an AI gave you is right?
Builds on:
- Describe how an assistant computes a number from your table
Your Maestro asks you to explain it in your own words and saves it as evidence when you do.
Describe how an assistant computes a number from your table
Where I teach it: Before you believe it · What does an AI do with your file before it gives you a number?
Your Maestro asks you to explain it in your own words and saves it as evidence when you do.
Read a short pandas calculation
Where I teach it: Before you believe it · How do you recompute an AI's number with pandas?
Your Maestro asks you to explain it in your own words and saves it as evidence when you do.
Identify what a row of a table represents
Where I teach it: What a row is · Is counting rows the same as counting sales?
Your Maestro asks you to explain it in your own words and saves it as evidence when you do.
Identify the denominator of an average or percentage
Where I teach it: What it divided by · What number did the AI divide by to get your percentage?
Builds on:
- Identify what a row of a table represents
Your Maestro asks you to explain it in your own words and saves it as evidence when you do.
Explain what happens to empty cells in a calculation
Where I teach it: What it left out · Does an empty cell count as zero in an average?
Your Maestro asks you to explain it in your own words and saves it as evidence when you do.
Who is this course for?
For anyone who asks ChatGPT, Copilot in Excel or Claude for numbers and plans to use them in a report: sales, budgets, surveys. If you work with Excel, a CSV or Google Sheets and have ever doubted a result, this is for you. You don't need to know how to code; knowing your own data is enough.
Ask your Maestro
Your Maestro is an AI that knows this course. Ask it about the first page and it answers right here, free.
You: Where do I start?
Your Maestro: From what you already know. Tell me what you've done with data, and I'll start this page from there.
Asking about: Answers from the page "How do you know if the number an AI gave you is right?"
Only this browser keeps what you ask here. How it works
What we'll cover
Before you believe it
What a row is
What it divided by
What it left out
Ask for it right, then decide
How long does it take?
45 minutes to 1.3 hours
A guide: you go at your own pace, and the course waits where you left off.
Common questions
- How do I know if the number an AI gave me is right?
- Ask it three questions before you use it: what counts as a row in your table, what it divided by, and which rows it left out. Then recalculate the number with a few lines of pandas, explained one by one. If your result and the AI's result differ, the gap is almost always in one of those three questions.
- Why does AI code well but get data analysis wrong?
- When you program, tests warn you when something breaks. With data, nothing does: the AI assumes what a row is, which rows to drop or what to divide by, and the number looks fine even when it is wrong. So you ask how many rows it read, which it dropped and why, and recalculate the number from the file.
- Who is this course for?
- For anyone who gets a number from an AI and is about to use it in a report: sales, budgets, surveys. If you work with Excel, a CSV or Google Sheets and ever doubted a result, this is for you. You do not need to code. You need to know your own data, and you already do.
- What will I be able to do when I finish?
- You will be able to recalculate a number an AI gave you, say what each row in your table represents, spot an average built on the wrong divisor, find rows that were left out or repeated, and decide how much to check based on what is at stake. You practice it all in 5 modules and 13 pages.
- Do I need a course, or can I learn this on my own?
- You can learn it on your own, and many people do. A course gives you the order: what to practice first, ready-to-use data, and exercises that show where you go wrong before it happens at work. This course is free, and your Maestro answers questions as you go. If you prefer going solo, the method still works.
- Is the course free?
- Yes, it is free. You can read all 13 pages without an account. If you sign in with your email and enroll with one tap, no card, you run the exercises in your browser and your Maestro answers on every page. Without an account, your Maestro answers a few questions on each page.
- Do I need to code to check what the AI did?
- No. The course code is short and works like a calculator: each line is explained on the page, and most of the time you only change a word or a number. It runs in your browser, so you install nothing. If a line is unclear, you ask your Maestro.
- Does it work if I use Copilot, ChatGPT or Claude?
- Yes. The three checks do not depend on the assistant. They work for any number an AI calculates from your table, whether in Excel, a CSV or Google Sheets. The tool changes, but the questions stay the same: what is a row, what was divided by, and what was left out.
- Do I have to upload work data?
- No. The whole course uses made-up data from a fictional hardware store in Guadalajara. When you want to practice with your own tables, first check what your company allows you to upload to each assistant. The course teaches you to check the number. It does not ask for your files.
How do I check what AI does? I teach it in Check what AI gives you in three steps.
What you get
- 5 modules and 13 pages, open whenever you want them.
Open to everyone: read all of it, and your Maestro, an AI, answers your questions on every page.
With a free account: your Maestro for the whole course, always on the page you're on, and the exercises run with nothing to install.
Words you'll meet
In the lessons, tap one to see what it means, or ask your Maestro about it.
Who's teaching you
Sergio Sánchez
I'm Sergio, chekos online. I'm a data architect, and I've spent more than ten years working with data in the Bay Area, mostly at mission-driven organizations: policy research first, then education, and now early childhood services. I grew up in Tijuana. In 2018 I started tacosdedatos to share what I was learning, and since then it's been a blog, a podcast, courses, guides, and a community. These days I spend a lot of my time building with AI agents and writing about how I organize my work around them. I share what I've learned; you take what's useful and make it yours.
See you in the course
Your AI and Your Data: Don't Let It Make Up the Number