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The World’s Worst Calculator

A new Lab for sharing mental models in an exploratory way.

The CEO is not supposed to code, but nonetheless I’ve been having fun shipping out a three-weekend project, which I call “Account.” It’s a storytelling tool with some simple calculations built in that you access via sliders. It’s not particularly novel, but it was interesting to make for Postlight Labs, and I would like to tell you about it.

You can visit it, or see the code.

What is it?

Account reads a text file like:

At your store {1-100:people} people each buy {12:apples} apples each week. That means that you need to buy {=people * apples:total_apples} apples a week, except {10:spoiled}% go bad…

And it gives you this:

There are a lot of interactive notebook tools but almost all of them are pretty complex. I wanted something that did basic algebra with very few options with plain text.

Why now?

I mean, why not? Writing low-stakes software is fun.

Also, my basic stack of communications tools has changed a lot in the last couple of months. I pitch a lot of new business for our company, and the most valuable sales tool I have is being in a room with a notebook, nodding and writing down what people say, making eye contact, and then asking them questions.

I can’t do that right now so I need to show my active listening in other ways. Most software for business is for making things, sometimes collaboratively (Google Docs, Figma, InVision), or it’s for telling people about what you made (PowerPoint, Google Slides, Keynote).

But there’s a space in the middle: Software for sharing mental models and thought processes that people can explore and play with. Like wireframes, but for business models and other ideas.

I really need tools in that space. Virtual sticky note boards are amazing, and we’re using them at work. But interactive shareable models that take a few minutes to glue together and mess with went out of fashion in the tech world of the 1970s and we could sure use them back right now.

I don’t take Account very seriously. I wanted to build and launch something and I wanted to update my React skills. That said, I just used it to build a model in five minutes that I presented to a client to show them why we have to keep a close eye on their content production goals. “And now,” I said, “because when you have a hammer everything looks like a nail…”

I moved the sliders around on a video call and said, “So you see, if we’re more efficient in our planning and keep our goals, we can save 2,500 hours of work.” Were they indulging me a little? Sure! But also it was a real exercise. They reacted to what I had to show them. They got what I was trying to convey and appreciated the effort. This is how we learn.

What’s next?

I built this app using JavaScript and React. There’s just a lot of JavaScript to tap into. So on weekend three I was able to add simple charting in about half an hour. So now my apples look like this:

Graph showing how much profit you'd make from selling apples, after inputting different variables like how many go bad and what they wholesale for.

I’ve also been exploring adding more more complex functions. There are libraries of statistical functions, astronomical functions, units (degrees, hogsheads, pound-forces, and farads). It’s pretty easy to rope those libraries and components into this framework. There are pie charts, agent simulations, and so forth.

As with all Postlight Labs projects, try it out, remix it, or tear it apart. It’s under an open-source MIT license, and we want to know your thoughts. Pull requests welcome.

Paul Ford is the CEO and co-founder of Postlight. Have an idea for software we can build together? Reach out to us at