1. https://www.investopedia.com/dictionary/
2. https://www.mathsisfun.com/money/internal-rate-return.html
3. P. McIntyre, D. Casella, C. Fonseca and P. Burr - Priceless! Uncovering the real costs of water and sanitation, IRC, 2014, 190 pp - https://www.ircwash.org/sites/default/files/2014_priceless_mcintyreetal_1.pdf
4. A. Kuyvenhoven and L. B. M. Mennes, "Guidelines for Project Appraisal. An Introduction to the Principles of Financial Economic and Social Cost-Benefit Analysis for Developing Countries", The Hague Government Printing Office, 1985, 190 pp