Lean Calculator
The Lean Calculator is a widget for the construction consultancy Meile + Stein. It shows a client what lean methods could save on their building project. Budget in, two gauges out.
It embeds into their site with one script tag and a custom element, without any network calls.
Built with
- Custom element, no runtime dependencies
- fully client-side, no network call, no tracking
- CSS custom properties for theming
How it works
Simple mode: a construction budget and one slider produce two gauges — schedule reliability and an indicative saving range.
Pro mode: lean measures per contract type, answered yes, partly or no. Broken down by dimension, with implementation costs and a net range.
In numbers
2026 2 Days
Process
- Client’s Excel model
- Ranges, not figures
- Two modes
- One script tag
The model came from an Excel prototype the client had already made. Every deviation from that original is written down in a correction log, so they can see what changed and why.
Whenever the calculator changes, it recomputes a set of known examples and compares them with the client's own figures. If one number is off, it says so (unit tests).
Hardest call
Show ranges, not exact figures. False precision would have been easier to build and impossible to defend: a number to two decimal places invites a discussion the model cannot survive.
The panel that explains the method and its sources sits inside the widget, not in a footnote.
What's next
Finished and delivered Further iterations likely
What can Iget out ofyour way?
Reach out