Editing Variable valve timing (section)

===Continuous versus discrete===
Early variable valve timing systems used discrete (stepped) adjustment. For example, one timing would be used below 3500 rpm and another used above 3500 rpm.

More advanced variable valve timing systems offer continuous (infinite) adjustment of the valve timing. Therefore, the timing can be optimized to suit all engine speeds and conditions.<ref name="wu2007"/><ref name="hong2004">Hong, H. (2004). Review and analysis of variable valve timing strategies - eight ways to approach. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 218(10), 1179–1200. Available at [https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.873.5451&rep=rep1&type=pdf citeseerx.ist.psu.edu] (accessed on 2022-04-29)</ref>