All-In-One Perpetual Calendar: 400 year Gregorian style
Which components do you know: day, date, month, year? If you know three, you can find the fourth. This calendar is extremely easy to use, although it looks pretty scary at first glance. First off, a note about leap years. Leap years are in bold. You need to pay attention to those because you use the January and February in bold for leap years. Use the normal type January and February for all other years.

Day of the week: Olivia was born June 30, 1962 and wants to know what day of the week that was. The column for June and the row for 30 cross at the letter C. Finding 1962 in the bottom of the table, she sees the letter C above it is in the row for Saturday.

Month: How many times did the superstitious have to worry about Friday the 13th in 1903? The column where 1903 resides is intersected by the row for Friday at the letter G. In the row for 13, G is underneath the normal year February, March and November. So there were three occurrences of Friday the 13th in 1903. The year wasn't a leap year. If you were looking up something like this for a leap year, you would ignore the normal February entry and consider only the bold February.

Date: When did the American Thanksgiving fall in 2000? It's been held on the fourth Thursday of November for many decades. In 2000's column, across from Thursday is the letter D. Under November, the letter D appears in the same row as 2, 9, 16, 23, and 30. So November 23rd was Thanksgiving in 2000.

Year: What years had or will have a Thursday, July 4th? July and 4 meet at F. In the row for Thursday, F is above 1957, 1963, 1968, and many other years. If looking up the possible years for a month-date-day combination in January or February, remember to be careful about leap years. As an examle, consider Tuesday, January 19th. The normal year January and 19 cross at D. In the row for Tuesday, D is above the normal years 1965, 1971, 1982. The bold leap year January and 19 cross at E. In the row for Tuesday, E is above the leap years 1960, 1988, 2016, etc.

If you cross-reference the components out of order, your results will be wrong most of the time. They'll be right some of the time and may give you a false feeling that you're doing it right. If you know the month and date, cross them first. If you know the year and day of the week, cross them first.

This style of perpetual calendar appeared in the Information Please Almanac at least as far back as the 1960s. You can extend this calendar's coverage forward or backward indefinitely by adding or subtracting 400 for each year entry and using that number instead of the year shown. In other words, 2002 has the same calendar as 1602, 2402, and 2802 under the Gregorian system. Be careful doing this. The Gregorian calendar wasn't adopted everywhere at the same time. You could look up a day of the week for an event in the 1600s British Empire and you'd be wrong!