"Place year over month. For 50 years calendar, 1971- 2020."
At the top, you slide the appropriate year tab to line up with the month. At the bottom, the numbers then align with the days of the week.
I found the brass calendar amongst my grandfather's things. From the looks of the graduation cap on the left, someone (one of my aunts?) graduated in 1971 and got this 50 year calendar to commemorate the occasion. Doesn't look like it's been used much in the past 41!
Between my iPhone and various notebooks, the way I keep track of days changes so often that it seems incredible to do it on one device for the greater part of your life.
Operating systems change all the time. But at least I know what the next nine years will look like.