About Us


Two brothers, Dan and Dean Linder, founded KnowledgeDoor with the dream of creating the kind of information and calculating resources that we wanted when we first started working in science and technology. With degrees in engineering, physics, and mathematics, as well as several years in research and teaching, we have worked thousands of problems between us and we know what it takes to consistently get the correct answer. We want to grow our Numerari app into a combination calculator/handbook that will be the first tool you reach for when you start solving a problem.

To do that, we know that Numerari has to be fast and easy to use. That is why we have multiple ergonomic keyboard arrangements so that you can pick the one that is most comfortable. That is why you can use previous results and expressions in your new calculations with just a single tap. We make use of pop-up keypads instead of deep menu hierarchies so that you can access critical functionality with one or two key taps. We added the intuitive "form interface" for graphing so that you could create graphs without having to enter commands and remember options. There are lots of programming tools for technical problems, but you don't want to have to write the equivalent of a small program to quickly explore back-of-the-envelope calculations.

To be the first calculation tool you reach for, Numerari has to help you check your work so that you consistently get correct answers. That is why we integrated units into all of Numerari's functionality and made them quickly available with pop-up keypads. Numerari is the first calculator, app or handheld, that allows you to use units as a routine part of your calculations. This allows unit consistency to be verified all the time and for unit conversions to be automatic. We have found through experience that verifying unit consistency is an indispensible tool for avoiding errors. It may take a little work to think through how to properly use units in a problem but it is always worth the effort.

Your calculations are only as good as the values that go into them. You need confidence in the values you are using and that is why the KnowledgeDoor website has over 25,000 values for the chemical elements with full citations indicating where those values were found. As we worked on that database, we were often shocked at how many values in standard handbooks can be close to a century old. Also, try our units and constants handbook with 384 units and 80 constants indexed by name, quantity, and group (for units such as "calorie" that have several related values). You can use all of these units and constants in our KnowledgeDoor website unit conversion calculators.

We have many exciting updates planned for your Numerari, and we hope that it will be an app that helps you throughout your career. Please help us improve Numerari by letting us know what you like or don't like and what features you wish you had for your work. Also, please consider taking a moment to give Numerari a star-rating or perhaps even a review.