Perpetual Calendar Breakthrough

A perpetual calendar is one that can be reused year after year. This Instructable presents what I consider to be a breakthrough design concept. Although various types of perpetual calendars have been around for a long time, none have replaced conventional calendars for everyday use. The ones available either require reference to a conventional calendar to set them or are difficult to read. My practical tent desk calendar is set by simply moving a slider to put the month over the year. The display of the days of the month is the same as on a conventional calendar, and the month can be found by checking which month (or months) are over the year of interest. The file “Comparison of Perpetual Calendars” describes how my practical perpetual calendar is uniquely different than any other that I have found.

Step 1: Look at the Components

These images show the face of the tent with the slider removed and the slider. The calendar has the following components:

· A table at the top with the days of the week. In this example, they are SMTWTFS.

· A window which displays seven columns of a 13-column slider.

· A 13-column slider which has a day-of-month table above a month table.

· A 7-column table of years below the window. In this example, there is room for 100 years to cover the entire 21st century.

The calendar is made from cardstock, and consists of two parts, the tent body and the slider. The face of the body has a table at the top with the days of the week and a table of years printed on the bottom, with a space between these two tables for the window. There is a slit on each side of the window to hold the slider. When the slider is threaded from the back through one of the slits and returned to the back through the other slit, the window displays seven columns of the slider. In the rows of months, the top row applies to January and February of a leap year, the middle two rows apply to March to December of all years, and the bottom row applies to January and February of a common year. To bring attention to leap years, JAN and FEB are in bold in the top row and leap years are also in bold in the year table. The calendar always displays 31 days for the month, with 29, 30 and 31 to be ignored as applicable.

This design can be adapted to make a pocket calendar. A calendar based on this design can be part of a planner, a photo holder, a key holder or a clock. I have also designed perpetual wall calendars that have a sheet for each month. My designs are documented in my book “Practical Perpetual Calendars – Innovative, Convenient and Green” by James R. Saltvold. You can view a pdf copy of it free of charge at https://archive.org/search.php?query=saltvold . My website, www.jamessaltvold.com , has a few designs that I have developed since my book was published in 2017.

The contents of the files below are:

“Single-Sheet Desk Calendar”: This is a pdf document that you can print and cut out the tent desk calendar shown above.

“Using Excel for Graphics”: This is a pdf document that describes how to use Excel to make the graphics for the calendar. Excel is not a powerful graphics program, but it is widely available and easy to use.

Step 2: Tools and Supplies

Tools:

Straight edge 12 inches long

Sharp utility knife - Scissors can be used instead of a utility knife, but cutting slits with scissors is difficult.

Cutting mat - In place of a cutting mat, I used a piece of scrap drywall. While writing this Instructable, I tried using a magazine and that worked well.

Bone folder, also called a paper scoring tool, or a scoring stylus - In place of a special tool, I used a small flat screwdriver.

Printer – I recommend having a print shop do the printing as most home printers are not capable of handling cardstock.

Supplies:

80 lb. or heavier glossy cardstock - One 8.5 by 11-inch sheet for each calendar that you want to make. A print shop should be able to supply suitable cardstock. If you need cardstock, a product you might consider purchasing is Hammermill HAM120023 Color Copy Digital Cover Paper, which is 8.5 by 11-inch 80 lb. glossy cardstock. According to the manufacturer’s website this is “A durable, cover weight sheet designed specifically for color copiers and color laser printers.”

0.5 to 0.75-inch wide tape - I recommend Scotch® Matte Finish Magic™ Tape. Total length required is three inches and almost any tape will work.

Step 3: Download and Print the PDF Document "Single-Sheet Desk Calendar"

For a sturdy calendar with an easy-to-move slider, I suggest using 80 lb. or heavier glossy cardstock. To make a trial calendar, you can use ordinary 20 lb. paper. You can print the file yourself or have a print shop do it. I am fortunate to live close to a print shop that does small quantities from either an uploaded file or from your memory stick.

Step 4: Cut Out the Calendar

First, extend Line #1 and Line #2 to both edges. Then cut along these lines to cut out the body of the calendar. Next, cut the two slits in the face to hold the slider. As indicated in the window, cut them a little short and then lengthen as required to obtain a good fit for the slider. Now cut two slits in the back to hold the piece that says “1800 to 1899” on one end and “1900 to 1999” on the other end. This is an optional piece that can be temporarily held in front of the 21st century table to check dates in the previous two centuries. Effectively, this piece extends the range of the calendar from 100 years to 300 years. By printing on both sides of this piece, the range of the calendar can be 500 years! However, for most applications, the 100-year table on the face of the calendar is all that is required.

Lastly, cut out the slider and the optional piece for the 19th and 20th centuries. Note that the corners are cut to facilitate threading into the slits.

Step 5: Assemble the Calendar

Fold the tent body along the three dashed lines. The ideal procedure is to draw the lines on the back, and score along these lines. After scoring, lay a straight edge along each line and fold. To save the step of drawing the lines on the back, score lightly on the front side and fold in the wrong direction about 20 degrees so that a fold line can be seen on the back. Then fold in the correct direction.

Next, insert the slider and then the piece for the 19th and 20th centuries. Lengthen the slits as required to obtain a good fit. As shown above, insert the centuries piece so that “1800 to 1899” and “1900 to 1999” can be seen from the back after it is in place. Finish assembling the calendar by joining the two ends together at the bottom. To maximize the width of the bottom, I suggest butting the ends together and taping them. Three pieces of tape 0.5 to 0.75 inches wide by an inch long are required. The tape goes on the inside where it does not show, so almost any kind will work.

Step 6: Enjoy Your Calendar

In addition to displaying the current month on your desktop, the perpetual calendar can be used to solve date problems. One is to find which day of the week your birthday is on for any year. Suppose your birthday is May 17, and you want to know the day of the week in 2030. Set May over the year column that contains 2030, and note that it will be on a Friday. You can also find the years that your birthday will be on a particular day of the week, say Sunday. Set 17 under Sunday, and under May note the years 2026, 2037, etc. Sometimes you can use the calendar to guess a date. A co-worker tells you on June 15, 2021 that today is her wedding anniversary. You forgot which year she was married, but you know it was on a Saturday. Set 15 under Saturday and under June note the years 2002, 2013 and 2019. You also know that she has been married for a few years, but less than 10. Therefore, she was married in 2013.