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The basics of learning to memorise the calendar have already been dealt with. Now we need to take a look at the intricacies of the day and date calculator. If we want to become real life day and date calculators, we’ve got to get the details right. If we get even one thing wrong, we get the wrong answer. So, although the calculation isn’t difficult, and although the figures are quite small, we have to actually take care of every little detail to make it work. It has to be water tight. One slip up and the result won’t be amazing, it’ll be depressingly, er … wrong.

## Leap years

If you want to tell the day for any date, you’ll have to take leap years into account. Dealing with leap years is actually very easy. First you have to determine whether or not a year actually is a leap year, and then it depends on whether the date is before the end of February. If it *is* a leap year, and if the date *is* earlier than the end of February, then all you have to do is subtract 1 from the total. In other words, the answer to the riddle will be one day earlier than you’ve already determined.

### But how do you tell if it *is* actually a leap year?

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The short answer is this: Any year that is evenly divisible by 4 is a leap year. You can ignore the first two digits (the 19), and just check that the last two are divisible by 4. So, for example, 1936 was a leap year, because 36 is evenly divisible by 4 (9 x 4 = 36). But 1958 wasn’t a leap year (58 divided by 4 is 14, with two left over). A year that is evenly divisible by 100 (for example, 1900) is a leap year *only* if it is also evenly divisible by 400.

For this reason, the following years are ** not** leap years: 1700, 1800, 1900, 2100, 2200, 2300, 2500, and 2600. This is because they are evenly divisible by 100 but

*not*by 400.

The following years ** are** leap years: 1600, 2000, 2400. This is because they

*are*evenly divisible by both 100 and 400.

For all practical purposes, you don’t need to bother with most of that, since you’ll generally be working with dates from 1900 onwards.

In a nutshell: if it can be divided evenly by 4 then it’s a leap year. Look at the two last digits. Divide by 4. If there’s no remainder, it’s a leap year. It’s the start of a century? Divide by 400. If there’s no remainder, it’s a leap year.

And to recap, if you’ve determined that the year in question *is* a leap year, and the date is in either January or February, then you need to subtract 1 from your total.

Example: say the date is 12th of February, 1916, you have 12 (for the date), plus 4 (for the month, making 16 … might as well ditch 14 of that total, leaving 2), and 6 (for the year, making a total of 8) … but hold on, 1916 *was* a leap year, and the date *was* in February, so you have to subtract 1 from the 8, making 7, which can also be ditched, of course … so you’re left with zero … which is Saturday.

Remember, every detail is important – even ignoring the *possiblity* that a year could be a leap year could bring a halt to your day and date calculator progress.

### Dates apart from the 20th century

If you want to use the day and date calculator accurately, there will be times when those dates aren’t from the 20th century, and you have to be aware of this. You might think this would get complicated now, working with different centuries. Actually, it’s just the same type of thing … with a tiny adjustment.

In 1753 Britain adopted the Gregorian calendar, so you can’t use this system for working out dates prior to 1753. However, from 1753 to 1799, all dates will work using the Year Keys for the 20th century, as long as you add 4 to the total for your calculation (from now on, I’ll call the 20th century Year Keys, the Basic Year Keys).

For dates from 1800 to 1899, again use the Basic Year Keys, but add 2 to the total.

This brings us to 1900 to 1999 – obviously that’s the 20th century, so the Year Keys are accurate.

For dates from 2000 to 2099, use the Basic Year Keys, but subtract 1 from the total.

In a nutshell:

1800-1899: the Basic Year Keys +2

1900-1999: the Basic Year Keys

2000-2099: the Basic Year Keys -1

That takes care of all dates since the introduction of the Gregorian calendar.

### Remembering the Year Keys

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Again, there’s more than one way to do this. For a start, all the years are two-digit numbers (ignore the 19-), so you already have a couple of ways of visualising them. You could use the Major System and right away you’d have an image for each year (1933 would be a mime artist, 1967 would be a jug, etc). Or you could use the 100 List. This way each year would be a character (1912 would be Father Christmas, 1958 would be Frankie Fraser, etc).

If you chose to use the Major System, you could link each year (that is, the Major System *image* for each year) with an image that tells you its number. For example (and remember, you’ll only need 7 images, because all the years are either zero or 1-6), you could have images like …

- a lifebelt for 0 (or a wheel, or a doughnut)
- a pencil for 1 (or a telegraph pole, or a skewer, or a tree)
- a swan for 2
- a shamrock for 3 (or a milking stool)
- a table for 4 (or a chair)
- a glove for 5 (or a starfish, or a five-pointed star)
- a gun for 6 (or a snowflake, or a beehive [think hexagons in honeycomb])

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Then, associate each year with the image you’ve chosen to represent the numbers 0-6. It’ll take a little while, but once it’s done you only have to revise it a few times and it’s yours for life!

Another way is to use the 100 List, and associate each character with the number images, as above.

Still another way is to write all the years down in groups, so you have all the zero years in one group, the 1 years in the next, and so on. Then, convert the years to characters – in other words, turn the groups into groups of *characters*. Then use a method to keep them all together. Link them all in some way, so you remember they’re all ‘3’ characters, or ‘5’ characters.

### Create a few little weird stories

You could visualise each group in your house, in a different room, and make up a little scenario for each group. Imagine them interacting with each other in various, ridiculous ways. Imagine one group in your kitchen, for example, and see the first character trying to cook something for them all. Then one decides to add something weird into the mix – maybe washing up liquid, or floor polish. Perhaps someone takes offence at this (not surprising, really), and you’ve added action to the scene.

Build it up from there. Just make sure you’re using your 100 List characters, and you can see them clearly and vividly, and they’re all interacting with each other. If it all ends up with lots of washing up liquid getting squirted all over the place, and people trying to eat stuff that’s frothing like bubble bath, great! You won’t find that easy to forget!

Do this for each group. One group could be outside in the garden. I can imagine a hose getting turned on suddenly and things getting chaotic and very wet! Maybe another group is squeezed into a cupboard under the stairs – that should create some memorable scenes. It doesn’t matter how ridiculous these things sound, or how crazy they look to you when you imagine them. Actually it does – the crazier the better! You *want* crazy! You want your characters to find themselves in strange, unusual, ridiculous situations, that way you won’t forget them.

Do whatever it takes to make the Year Keys memorable. Use objects (a doughnut, a shamrock, a beehive, etc) and associate those objects in strange or weird images, or gather your characters into groups and construct a lively scenario for each group. Whatever method you use, you should soon be able to see something in your mind that tells you immediately that 1933 is a 6 year, for example, or 1984 a zero year.

The amazing thing is that once you’ve spent some time associating the years with the Year Keys, you’ll soon just know them, without thinking of the link you used. Your natural memory takes over and you automatically learn the Year Keys without any real effort!

### Performing day and date calculator magic!

No-one’s saying this is an easy thing to do. To be a real-life day and date calculator takes some work. You have to learn how the calculation works, you have to associate (i.e. learn) the Basic Year Keys, you have to get used to dealing with leap years and dates apart from the 20th century. There’s a lot of different things to take into account. But none of it is particularly difficult.

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You might find it difficult to do the calculations at first. You might not be able to do it quickly (I’d be surprised if you could!). You might find the whole thing challenging. But this is one amazing ‘trick’ to be able to do, and it has real world uses as well as just being something unusual for you to use to show off your memory power. It’s always useful to be able to put a day to any date. It doesn’t have to be to tell somebody that he was born on a Friday!

It could be a situation where you’re asked to be somewhere on the 22nd of October and you’re able to say, immediately, “Sorry, I can’t make that – the 22nd is a Thursday, I’ll be taking the kids bowling, we always go on a Thursday”. Now *that’s* kinda useful, being able to put a day to a date in a situation like that, you think?

*Can I check the facts, just to make sure?*

Sure you can! There are plenty of websites that have day and date calculators, and sometimes many other types of calculators as well. One such site is Easycalculation. Just enter the date in the boxes and click on ‘Go’ to set the day and date calculator into action and see the correct day of the week displayed. Another is CalculatorCat. You want one more? MathsIsFun. Pretty soon you won’t need any of them. Once you’ve been doing this for a while, you’ll be totally confident of your ability.