In April 1900, Professor L. A. Grosclaude of Geneva proposed the Invariable Calendar, New Era Calendar or Normal Calendar with 12 months and four 91-day quarters of exactly 13 weeks. An additional day, termed New Year's Day, that was not any day of the week and not part of any month, would occur between December 31 and January 1. Another such day is inserted between June 31 and July 1 on leap years.