We shall find the day on 1st April, 2001. 1st April, 2001 = (2000 years + Period from 1.1.2001 to 1.4.2001) Odd days in 1600 years $=0$ Odd days in 400 years = 0 Jan. Feb. March April $(31+28+31+1)$
Explanation as extracted from the printed page; notation may be imperfect.