My grandmother had a small desk paper weight sliding calendar from the 60s that she got as a promotional item from a bank. One side had the calendar and the slider and of course the bank name. The other side had a cheat sheet for year/month and what to set things to if you got lost. Think there were some plastic bits to clip over the days that were not in the month but those were lost to time. Think Matt Parker had a vid a few years ago on reusing calendars from previous years. 14 combinations I think was the total number of calendars you had to keep. But I could be remembering wrong.

Yes, it's 14: the year can begin on one of 7 days (7 possibilities), and then it contains either 365 or 366 days (2 possibilities), for a total of 14.

Exactly, you need another calendar in order for this calendar to work.

Wall calendars often have a horizontal stripe with a small window highlighting the current date. That would help solve the problem of forgetting to update it. You'd still need to remember how many days there are in the current month and you need to know the current date and day of the week to set it up but at least it seems workable.

It would work so much better if the frame had weekdays.

>You need to remember to slide the frame every month

And if you have a wall calendar you have to remember to tear down the page of the previous month every month...

Except the wall calendar has the current month on it in big letters, so all you need to know is what month it is. This thing does not tell you if it's showing you the days for Jun or Jul

also the entire point of a wall calendar is that you can make notes on specific days, isn't it?

> also the entire point of a wall calendar is that you can make notes on specific days, isn't it?

Which is still doable for this design, provided the backing is a whiteboard.

maybe this is just a design thing to keep as an accessory with no real value

Yes, I forgot to tear off the month 29 days ago so every time I look at the calendar I keep thinking it's still May.

It’s not nearly that complicated unless you just outright have no idea how many days are in a given month. Not sure how many adults don’t know that answer, but if you struggle to remember whether June has 30 or 31 days perhaps this calendar isn’t for you.

It’s not for me either as I see no value in a physical calendar, but I’d imagine the people who do see that value are the same type of people who are aware that June has … let me just pull out my phone real quick… 30 days.

> It’s not nearly that complicated unless you just outright have no idea how many days are in a given month. Not sure how many adults don’t know that answer

Please straight up ask ten people, even if your circles are on average highly educated, and see how many know an arbitrary month (not significant ones like February, or December where the 31st is new year's) without having to think about it or count knuckles. Asking about the current or an adjacent month might also be something they remember from recently seeing calendars that tell you this information.

I think it's very uncommon to have this memorized to the point where using a calendar that doesn't tell you is as easy as using one that does.

My child recently learned this in school, in first grade. I just assume everyone knows it.

There's an English jingle that I was taught (1970s), and my child also:

   Thirty days hath September, April, June and November.
   All the rest have thirty one, save February alone
   Which has twenty eight days clear, and twenty nine each leap year.

(ok, the "hath" part was what I was taught, I think he learned "has" :-)

(edit: in Australia, for reference)

>I think it's very uncommon to have this memorized

I think this might be a cultural thing. A friend of mine from Taiwan was perplexed I didn't have this memorized, my reaction was the same as yours.

> without having to think about it or count knuckles.

Why is this constraint necessary? If you can even so much as think about it or count knuckles (let alone that you happen to have memorized the number of days per month), then this calendar is useful.

From my understanding the cal aligns day-of-week to day-of-month but there is no slider to adjust for 28 or 29 or 30 or 31 days.

Doing the knuckle dance every time you glance at it, to know whether to change the month already, seems annoying. (Yeah you'd memorize it for that month after a bit, but still you have to pay attention.)

I don't think there is any correlation with level of education. I truly don't understand how people don't know this. There are a total of 12 months and the days per month absolutely never change outside of the occasional leap year in February.

What's wrong with counting on knuckles? You adjust your calendar with this contraption once per month.

> I truly don't understand how people don't know this.

And yet it's true. It would take me a lot of thinking to answer how many days are in an arbitrary month. And I'd probably only be 80% confident. I truly don't understand how I don't know this either. But I've never made an effort to learn it, nor has it been a problem.

Is it just once a month though? From my understanding the cal aligns day-of-week to day-of-month but there is no slider to adjust for 28 or 29 or 30 or 31 days.

Doing the knuckle dance every time you glance at it, to know whether to change the month already, seems annoying. (Yeah you'd memorize it for that month after a bit, but still you have to pay attention.)

There is an old trick that you can do with your knuckles: https://upload.wikimedia.org/wikipedia/commons/thumb/9/9b/Mo...

> It’s not nearly that complicated unless you just outright have no idea how many days are in a given month.

Unless you work closely with dates, asking somebody "how many days in April" will result in a calendar check, a song or a them doing something odd with their knuckles.

I honestly think most people know how many days in each month..

But yeah, the point still stands. Having a calendar actively has wrong number of days is very misleading and counterproductive even if one knows how many there are supposed to be. Not to mention it doesn't even have month shown.

For some months like February (unusual), October (Halloween), or December (New Year's Eve) I remember them.

But for the other months I sing the song. Takes about ten seconds, required monthly at most. I think this is pretty common.

Interesting.

I personally just remember the cutoff point (7/8), and before that odd months have 31, after it even months have 31 days. It eventually became "muscle" memory.

For me at least, once I hit my thirties I had just kind of memorized them all by osmosis.

What's wrong with counting on your knuckles for the 12 total times per year that you need to adjust this calendar?