NOPAT calculation

I’m really confused in calculating NOPAT when reading the EVA technical article.
https://www.accaglobal.com/gb/en/student/exam-support-resources/professional-exams-study-resources/p5/technical-articles/economic-value-added-part1.html

What I understand is that
1)accounting depreciation and amortisation should be added back due to it being a non-cash expense and only economic depreciation and amortisation should be deducted.
2) For development & research expenditure should be added back as it brings long term value to the company

What I don’t understand:
Why do we need to minus the amortisation charge on development & research expenditure in the calculation on NOPAT? Shouldn’t it be added back since its accounting amortisation?