Learn by watching and reading materials released by great system thinkers.

Ludwig von Bertalanffy

https://www.amazon.com/s/ref=dp_byline_sr_ebooks_1?text=Ludw...

John Seddon

https://youtu.be/hbNsQFd8DQw

https://youtu.be/kjKG011gsJ4

https://youtu.be/FbmuqYRi8z4

Theory of Constraints

https://www.amazon.com/dp/B002LHRM2O The Goal / Eli Goldratt

https://www.amazon.com/dp/B00KYW1L66 Necessary but Not Sufficient / Eli Goldratt

https://www.amazon.com/dp/0884271137 It's Not Luck / Eli Goldratt

https://www.amazon.com/dp/B00408ALES Isn't it Obvious? / Eli Goldratt

https://www.amazon.com/dp/B002LHRM2E Critical Chain / Eli Goldratt

https://www.amazon.com/dp/B004THZ9VK Be Fast or Be Gone / Andreas Scherer

https://www.amazon.com/dp/1499660901 Hanging Fire / Jeff Cox

https://www.amazon.com/dp/1439158932 Velocity / Dee Jacob

https://www.amazon.com/dp/B00XKX1FEO Epiphanized / Bob Sproull & Bruce Nelson

https://www.amazon.com/dp/B0185JFYEO Focus and Leverage / Bob Sproull & Bruce Nelson

A full list of books on ToC here http://www.tocico.org/?page=toc_books

Russell L. Ackoff

https://www.amazon.com/s/ref=dp_byline_sr_book_1?search-alia...

Gerald M. Weinberg

https://www.amazon.com/Gerald-M.-Weinberg/e/B00459FFAC/

Philip B. Crosby

https://www.amazon.com/Philip-B.-Crosby/e/B001HD360A

Peter M. Senge

https://www.amazon.com/Peter-M.-Senge/e/B000AQ8R86/

And many more, most of which are mentioned by the above in their work.

For some useful theory for estimation and planning of projects, Eli Goldratt wrote amazing content in the book "Critical Chain" which is an easy to read novel.

Should you find yourself developing this tool further, these books will give you an edge that most other tools lack -

http://www.amazon.com/Critical-Chain/dp/B002LHRM2E/

http://www.amazon.com/Be-Fast-Gone/dp/B004THZ9VK/

http://www.amazon.com/CCPM-3rdEd/dp/1608077349/