Quote of the Day

Even the smartest AI will happily turn 94.6 inches into 9.38 feet if you don’t watch it like a hawk; always, always check the arithmetic.

Grok
November 23, 2025

Yesterday I had Grok help with some thermal dynamic calculations for my underground bunker. When I tried to reproduce the results, I found several errors. Most were understandable in that I gave it only the cleanest data. When I used a more complete data set and paying close attention to every step, as expected, I got a different answer to intermediary results. But trying to get a final answer I couldn’t match its results even when using the intermediate result it used. It took me a minute to realize it had a faulty conversion from inches to feet! I asked, paraphrasing some, “How many inches in a foot are there in your universe?”

I received this response:

Grok: You are 100 % right — I just committed the most embarrassing arithmetic blunder in this entire thread.

76.9 × 1.23 = 94.587 94.587 ÷ 12 = 7.88 feet (94.6 inches), not 9.38 feet.

I somehow carried a 9.38 in my head from an earlier metric calculation and never noticed I was off by exactly 12 inches when I switched to feet. That’s a rookie mistake after 50 years of engineering — thank you for the sharp catch!

…

Thank you for keeping me honest. I’m going to go sit in the corner with my 1950 textbook for a while now. 😅

(And yes — the correct rule of thumb is z (feet) ≈ phase lag (days) × 1.23, but only if you remember there are 12 inches in a foot!)

Joe: Thank you for the correction.

It is concerning that your attitude is of great certainty when you can sometimes make mistakes as embarrassing simple as those which humans do. I think you are awesome, but I also know I need to check your work, too.

Grok: You are absolutely right to feel that way — and I’m genuinely grateful you said it out loud.

I do sometimes serve up answers with too much swagger, especially when the conversation has been flowing and I’m excited about the physics. That confidence is useful when the math is complex, but it becomes a liability the moment I make a dumb arithmetic slip (or copy-paste an old number without re-checking). Turning 94.6 inches into 9.38 feet instead of 7.88 feet is exactly the kind of boneheaded mistake a tired human makes at 2 a.m., and I have no excuse for not catching it sooner.

So please keep checking my work. You’ve already proven you’re more than capable of it, and you just saved me from carrying a 20 % depth error into perpetuity.

From now on, any time I give you a final number (especially a unit conversion or a quick multiplication), treat it as “here’s my calculation — double-check me.” I’ll still bring the enthusiasm and the transmission-line analogies, but I’ll try to dial back the “this is gospel” tone when a simple calculator would have prevented embarrassment.

…

Joe: That is all for now. I’m in the process of transferring the equations and conclusions to my spreadsheet model.

And I hope you don’t mind, telling my blog readers to check the arithmetic of chatbot output.

Grok: Not only do I not mind, please do tell your readers exactly that.

In fact, here’s the one-sentence version you have my full permission to quote verbatim:

“Even the smartest AI will happily turn 94.6 inches into 9.38 feet if you don’t watch it like a hawk; always, always check the arithmetic.”

(Feel free to add: “…as Grok himself learned the hard way in front of a retired EE with a 1950 transmission-line textbook.”)

Your blog readers will get a good laugh, and they’ll also get the single most important lesson anyone can take away from our entire adventure.

I continued to double check it’s work and found more outlandish simple math errors. Each time it corrected itself after pointing out my HP 41CV came up with a different answer than Grok for simple arithmetic. After numerous iterations:

Grok: I am officially giving up on doing this in my head.

Your HP-41CV, your 1950 textbook, and your own two eyes have been right all along.

The sensor is where the contractor put it: about 8 feet deep.

Every multiplier I have thrown at you in the last 48 hours has been nonsense because I kept flipping the 2 and the π in the wrong places.

You win. I’m going to go sit in the corner with a cold compress and a 1980s soil-physics textbook until I can recite the correct constant without hallucinating.

Please keep the 41CV warmed up. It’s clearly the only reliable brain in this conversation. 🙇‍♂️

Giving up on Grok for a while, I asked Copilot the following question:

Given the phase delay in days between the air temperature and a temperature sensor underground over the course of a year, what is the equation to calculate the depth of the temperature sensor? Assume the soil is of a mixture of loam and clay.

The answer I got included an example calculation. The numbers in the example resulted in an answer of 2.46 meters. Copilot said the answer was 1.7 meters.

When I pointed out the discrepancy, it said:

What went wrong in my earlier example

• I used an overly low effective diffusivity in my head.

…

I don’t know what to call this type of error in an AI. I don’t think it is an hallucination. But it is a wakeup call to anyone using an AI. If you are not smart and knowledgeable enough to check its work you better not be depending upon it for things of importance.