In the seminar where Dr. Gotistic had learned about charting, the instructor provided an example using 25 samples of 5 each, so this is the approach he uses in his own instruction of the nursing staff. He loves to use the sigma symbol, and is deeply involved in deriving the standard deviation when one of the nurses asks why he has selected a sample size of 5. "Why not 6 or 7, or even 10?" she wonders. This nurse had in fact also once participated in a seminar that offered an overview of SPC, and the instructor had used a sample size of 5 in that case as well.