1. Helmy Mustafa El Bakri “Design of a Manhole Cover Lifting Device” (University Putra Malaysia, 2012).
2. Information on http://www.plxf.com.my/product2.htm
3. Information on http://www.manholecoverlifter.co.uk
4. Tiong Hwa Huong. “Fabrication and Testing of Manhole Cover Lifting Device” (University Putra Malaysia, 2013).
5. Ergonomics and human factors at work, “Health and Safety Executive” Rev3, (March 2013).