In 1959 Dr. Herbert Sinner, a German chemical engineer and head of detergents development at Henkel, illustrated the cleaning process as a circle with four sectors representing chemicals, mechanical action, temperature and time. Sinner's Circle is still used when describing cleaning processes and how varying the size of some sectors will affect the other sectors.
<a href="//commons.wikimedia.org/wiki/User:KJG2007" title="User:KJG2007">Johan Gustafsson</a>
CC BY 4.0
<span class="int-own-work" lang="en">Own work</span>