<prompt> Translate the following text to EnglishBaada ya miaka miwili ya kukusanya data, au angalau pointi za data 20, chati ya udhibiti inapaswa kudumishwa kwa kutumia tu pointi za data za hivi karibuni.  <response>: After two years of data collection, or a minimum of 20 data points, the control chart should be maintained using only the 20 most recent data points. 